0001193125-26-209067 | 10-Q | XBRL Viewer

Income Tax

6 Months Ended

Mar. 31, 2025

G. Income Tax

Effective Tax Rate


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(Dollars in millions)
(Provision) benefit for income taxes	$	(44	)	$	(49	)	$	(81	)	$	(90	)
Effective tax rate		37	%		32	%		34	%		30	%

For the three and six months ended March 31, 2026, the provision for income taxes included a net discrete tax expense of $7 million and $11 million, respectively, primarily related to withholding taxes on dividend distribution. For the three and six months ended March 31, 2025, the provision for income taxes included a net discrete tax expense of $7 million and $9 million, respectively.

Income tax in Interim Periods

The Company records its tax provision or benefit on an interim basis using an estimated annual effective tax rate. This rate is applied to the current period ordinary income or loss to determine the income tax provision or benefit allocated to the interim period. The income tax effects of unusual or infrequent items are excluded from the estimated annual effective tax rate and are recognized in the impacted interim period. Losses from jurisdictions for which no benefit can be recognized are excluded from the overall computations of the estimated annual effective tax rate and a separate estimated annual effective tax rate is computed and applied to ordinary income or loss in the loss jurisdiction.

Valuation allowances are provided against the future tax benefits that arise from the deferred tax assets in jurisdictions for which the Company expects that no benefit can be recognized. The estimated annual effective tax rate may be significantly impacted by non-deductible expenses and the Company’s projected earnings mix by tax jurisdiction. Adjustments to the estimated annual effective income tax rate are recognized in the period when such estimates are revised.

Uncertainties

Cabot and certain subsidiaries are under audit in a number of jurisdictions. In addition, certain statutes of limitations are scheduled to expire in the near future. It is reasonably possible that a change in the unrecognized tax benefits may also occur within the next twelve months related to the settlement of one or more of these audits or the lapse of applicable statutes of limitations. However, an estimated range of the impact on the unrecognized tax benefits cannot be quantified at this time.

Cabot files U.S. federal and state and non-U.S. income tax returns in jurisdictions with varying statutes of limitations. The 2022 through 2024 tax years generally remain subject to examination by the IRS and various tax years from 2019 through 2024 remain subject to examination by the respective state tax authorities. In foreign jurisdictions, various tax years from 2006 through 2025 remain subject to examination by their respective tax authorities.

- Definition

The entire disclosure for income tax.

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+ Details

Contingencies - Additional Information (Detail) - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Respirator Liabilities [Member]
Loss Contingencies [Line Items]
Respirator reserve	$ 32	$ 33

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Supplier Financing Programs - Additional Information (Details) - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Supplier Finance Program [Line Items]
Outstanding payment obligations to financial institutions related to supplier financing programs	$ 12	$ 13
Supplier Finance Program, Obligation, Current, Statement of Financial Position [Extensible Enumeration]	Accounts Payable and Accrued Liabilities, Current	Accounts Payable and Accrued Liabilities, Current

Contingencies	6 Months Ended
Mar. 31, 2026
Commitments and Contingencies Disclosure [Abstract]
Contingencies	F. Contingencies Respirator Liabilities Cabot has exposure in connection with a safety respiratory products business that a subsidiary acquired from American Optical Corporation (“AO”) in an April 1990 asset purchase transaction. The subsidiary manufactured respirators under the AO brand and disposed of that business in July 1995. In connection with its acquisition of the business, the subsidiary agreed, in certain circumstances, to assume a portion of AO’s liabilities, including costs of legal fees together with amounts paid in settlements and judgments, allocable to AO respiratory products used prior to the 1990 purchase by the Cabot subsidiary. In exchange for the subsidiary’s assumption of certain of AO’s respirator liabilities, AO agreed to provide to the subsidiary the benefits of: (i) AO’s insurance coverage for the period prior to the 1990 acquisition and (ii) a former owner’s indemnity of AO holding it harmless from any liability allocable to AO respiratory products used prior to May 1982. As more fully described in the 2025 10-K, the respirator liabilities generally involve claims for personal injury, including asbestosis, silicosis and coal worker’s pneumoconiosis, allegedly resulting from the use of respirators that are alleged to have been negligently designed and/or labeled. At no time did this respiratory product line represent a significant portion of the respirator market. In addition to Cabot’s subsidiary, other parties are responsible for significant portions of the costs of these respirator liabilities (as defined in the 2025 10-K, the “Payor Group”), leaving Cabot’s subsidiary with a portion of the liability in only some of the pending cases. As of March 31, 2026 and September 30, 2025, the Company had $32 million and $33 million, respectively, reserved for its estimated share of liability for pending and future respirator claims and for defense costs, the majority of which the Company expects to incur over the next ten years. The reserve is included in Other liabilities and Accounts payable and accrued liabilities on the Consolidated Balance Sheets. The Company’s current estimate of the cost of its share of pending and future respirator liability claims is based on facts and circumstances existing at this time, including the number and nature of the remaining claims. Developments that could affect the Company’s estimate include, but are not limited to, (i) significant changes in the number of future claims, (ii) changes in the rate of dismissals without payment of pending claims, (iii) significant changes in the average cost of resolving claims, including potential settlements of groups of claims, (iv) significant changes in the legal costs of defending these claims, (v) changes in the nature of claims received or changes in the Company’s assessment of the viability of these claims, (vi) trial and appellate outcomes, (vii) changes in the law and procedure applicable to these claims, (viii) the financial viability of the parties that contribute to the payment of respirator claims, (ix) exhaustion or changes in the recoverability of the insurance coverage maintained by certain members of the Payor Group, or a change in the availability of the indemnity provided by a former owner of AO, (x) changes in the allocation of costs among the various parties paying legal and settlement costs, and (xi) a determination that the assumptions that were used to estimate Cabot’s share of liability are no longer reasonable. The Company cannot determine the impact of these potential developments on its current estimate of its share of liability for existing and future claims. Because reserves are limited to amounts that are probable and estimable as of a relevant measurement date, and there is inherent difficulty in projecting the impact of potential developments on Cabot’s share of liability for these existing and future claims, it is reasonably possible that the liabilities for existing and future claims could change in the near term and that change could be material. Other Matters The Company has various other lawsuits, claims, and contingent liabilities arising in the ordinary course of its business and with respect to its divested businesses. The Company does not believe that any of these matters will have a material adverse effect on its financial position; however, litigation is inherently unpredictable. Cabot could incur judgments, enter into settlements, or revise its expectations regarding the outcome of certain matters, and such developments could have a material impact on its results of operations in the period in which the amounts are accrued or its cash flows in the period in which the amounts are paid.

Contingencies

6 Months Ended

Mar. 31, 2026

Commitments and Contingencies Disclosure [Abstract]

Contingencies

F. Contingencies

Respirator Liabilities

Cabot has exposure in connection with a safety respiratory products business that a subsidiary acquired from American Optical Corporation (“AO”) in an April 1990 asset purchase transaction. The subsidiary manufactured respirators under the AO brand and disposed of that business in July 1995. In connection with its acquisition of the business, the subsidiary agreed, in certain circumstances, to assume a portion of AO’s liabilities, including costs of legal fees together with amounts paid in settlements and judgments, allocable to AO respiratory products used prior to the 1990 purchase by the Cabot subsidiary. In exchange for the subsidiary’s assumption of certain of AO’s respirator liabilities, AO agreed to provide to the subsidiary the benefits of: (i) AO’s insurance coverage for the period prior to the 1990 acquisition and (ii) a former owner’s indemnity of AO holding it harmless from any liability allocable to AO respiratory products used prior to May 1982. As more fully described in the 2025 10-K, the respirator liabilities generally involve claims for personal injury, including asbestosis, silicosis and coal worker’s pneumoconiosis, allegedly resulting from the use of respirators that are alleged to have been negligently designed and/or labeled. At no time did this respiratory product line represent a significant portion of the respirator market. In addition to Cabot’s subsidiary, other parties are responsible for significant portions of the costs of these respirator liabilities (as defined in the 2025 10-K, the “Payor Group”), leaving Cabot’s subsidiary with a portion of the liability in only some of the pending cases.

As of March 31, 2026 and September 30, 2025, the Company had $32 million and $33 million, respectively, reserved for its estimated share of liability for pending and future respirator claims and for defense costs, the majority of which the Company expects to incur over the next ten years. The reserve is included in Other liabilities and Accounts payable and accrued liabilities on the Consolidated Balance Sheets.

The Company’s current estimate of the cost of its share of pending and future respirator liability claims is based on facts and circumstances existing at this time, including the number and nature of the remaining claims. Developments that could affect the Company’s estimate include, but are not limited to, (i) significant changes in the number of future claims, (ii) changes in the rate of dismissals without payment of pending claims, (iii) significant changes in the average cost of resolving claims, including potential settlements of groups of claims, (iv) significant changes in the legal costs of defending these claims, (v) changes in the nature of claims received or changes in the Company’s assessment of the viability of these claims, (vi) trial and appellate outcomes, (vii) changes in the law and procedure applicable to these claims, (viii) the financial viability of the parties that contribute to the payment of respirator claims, (ix) exhaustion or changes in the recoverability of the insurance coverage maintained by certain members of the Payor Group, or a change in the availability of the indemnity provided by a former owner of AO, (x) changes in the allocation of costs among the various parties paying legal and settlement costs, and (xi) a determination that the assumptions that were used to estimate Cabot’s share of liability are no longer reasonable. The Company cannot determine the impact of these potential developments on its current estimate of its share of liability for existing and future claims. Because reserves are limited to amounts that are probable and estimable as of a relevant measurement date, and there is inherent difficulty in projecting the impact of potential developments on Cabot’s share of liability for these existing and future claims, it is reasonably possible that the liabilities for existing and future claims could change in the near term and that change could be material.

Other Matters

The Company has various other lawsuits, claims, and contingent liabilities arising in the ordinary course of its business and with respect to its divested businesses. The Company does not believe that any of these matters will have a material adverse effect on its financial position; however, litigation is inherently unpredictable. Cabot could incur judgments, enter into settlements, or revise its expectations regarding the outcome of certain matters, and such developments could have a material impact on its results of operations in the period in which the amounts are accrued or its cash flows in the period in which the amounts are paid.

- Definition

The entire disclosure for loss and gain contingencies. Describes any existing condition, situation, or set of circumstances involving uncertainty as of the balance sheet date (or prior to issuance of the financial statements) as to a probable or reasonably possible loss incurred by an entity that will ultimately be resolved when one or more future events occur or fail to occur, and typically discloses the amount of loss recorded or a range of possible loss, or an assertion that no reasonable estimate can be made.

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+ Details

Restructuring (Tables)

6 Months Ended

Mar. 31, 2026

Restructuring and Related Activities [Abstract]

Restructuring Activities and Related Reserves

Details of all restructuring activities and related reserves during the three and six months ended March 31, 2026 were as follows:


	Severance and Employee Benefits			Non-Cash Asset Impairment and Accelerated Depreciation			Other			Total
	(In millions)
Reserve at September 30, 2025	$	7		$	—		$	1		$	8
Charges		4			3			—			7
Cost charged against assets		—			(3	)		—			(3	)
Cash paid		(3	)		—			(1	)		(4	)
Reserve at December 31, 2025	$	8		$	—		$	—		$	8
Charges		3			5			—			8
Cost charged against assets		—			(5	)		—			(5	)
Cash paid		(2	)		—			—			(2	)
Reserve at March 31, 2026	$	9		$	—		$	—		$	9

Recorded Restructuring Expense

Cabot’s restructuring expense was recorded in the Consolidated Statement of Operations for the three and six months ended March 31, 2026 and 2025 as follows:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Cost of sales	$	7	$	2	$	13	$	2
Selling and administrative expenses		1		—		2		—
Research and technical expenses		—		1		—		1
Total	$	8	$	3	$	15	$	3

Income Tax - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Income Taxes [Line Items]
Net discrete tax expense (benefit)	$ 7	$ 7	$ 11	$ 9
United States Internal Revenue Service (IRS) [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2022 2023 2024
State Tax Authorities [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2019 2020 2021 2022 2023 2024
Foreign Jurisdictions [Member]
Income Taxes [Line Items]
Tax years remain subject to examination			2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025

Significant Accounting Policies (Policies)	6 Months Ended
Mar. 31, 2026
Accounting Policies [Abstract]
Recently Adopted Accounting Standards:	Recently Adopted Accounting Standards: In December 2023, the FASB issued a new standard, Improvements to Income Tax Disclosures. The new guidance requires, on an annual basis, additional disaggregation in the rate reconciliation, disclosure of income (loss) from continuing operations before income taxes, and disclosure of income tax expense and cash taxes paid by jurisdiction (federal, state, and foreign). The Company adopted the new standard on October 1, 2025 and will provide the disclosures required by the standard in the fiscal 2026 Form 10-K. The adoption of the standard is not expected to have a material impact on the Company’s Consolidated Financial Statements. In November 2023, the FASB issued a new standard, Improvement to Reportable Segment Disclosures. The new guidance enhances the disclosure of significant reportable segment expenses. The Company adopted the standard for the fiscal year ended September 30, 2025 and for interim reporting periods beginning with the quarter ended December 31, 2025. See Note L for disclosures related to the Company's reportable segments. The adoption of the standard did not have a material impact on the Company’s Consolidated Financial Statements. Recent Tax Legislation On July 4, 2025, the U.S. federal government enacted the One Big Beautiful Bill Act (“OBBBA”). The OBBBA contains significant changes to federal tax law, such as the permanent extension of certain expiring provisions of the Tax Cuts and Jobs Act, modifications to the international tax framework and the restoration of favorable tax treatment for certain business provisions. The provisions in the legislation are generally effective for the Company beginning in fiscal year 2026. The impact of these changes was not material to the Company’s Consolidated Financial Statements for its interim period ending March 31, 2026. Recently Issued Accounting Standards Not Yet Adopted In November 2024, the FASB issued a new standard, Expense Disaggregation Disclosures. The new guidance requires quantitative and qualitative disclosure of certain cost and expense categories in the notes to the financial statements for interim and annual reporting periods. The new standard is effective for the Company's fiscal 2028 annual and interim reporting periods, with early adoption permitted. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on the Company’s Consolidated Financial Statements. In December 2025, the FASB issued amendments to the interim reporting guidance: Interim Reporting — Narrow-Scope Improvements. The guidance improves the navigability of the required interim disclosures and clarifies when that guidance is applicable. The guidance is effective for the Company's interim reporting periods beginning on October 1, 2028. The amendments can be applied either (1) prospectively or (2) retrospectively to any or all prior periods presented in the financial statements. The Company is currently evaluating the impact of the adoption of this amendment on the Company’s Consolidated Financial Statements. In September 2025, the FASB issued a new standard, Intangibles—Goodwill and Other—Internal-Use Software: Targeted Improvements to the Accounting for Internal-Use Software, which is intended to modernize the accounting for the costs of internal use software given the evolution of software development to the incremental and iterative development method. The amendments remove all references to prescriptive and sequential development stages and require an entity to start capitalizing software costs when management has authorized and committed to funding the software project, it is probable that the project will be completed, and the software will be used to perform the function intended. The amendments are effective for annual and interim reporting periods beginning on October 1, 2028. Early adoption is permitted as of the beginning of an annual reporting period with the amendments to be applied using a prospective, modified retrospective, or retrospective transition approach. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on the Company’s Consolidated Financial Statements. In December 2025, the FASB issued a new standard, Accounting for Government Grants Received by Business Entities. The standard establishes authoritative guidance on the accounting for government grants received by business entities, including guidance for a grant related to an asset and a grant related to income. The new standard allows for a number of accounting policy elections to be made upon adoption and be applied to the subsequent grants received on a prospective basis. The new standard is effective for the Company’s annual and interim reporting period beginning on October 1, 2029. The new standard provides entities with a choice of modified prospective, modified retrospective, and retrospective adoption approach. The Company is currently evaluating the impact of the adoption of this standard on its Consolidated Financial Statements.

Significant Accounting Policies (Policies)

6 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Recently Adopted Accounting Standards:

In December 2023, the FASB issued a new standard, Improvements to Income Tax Disclosures. The new guidance requires, on an annual basis, additional disaggregation in the rate reconciliation, disclosure of income (loss) from continuing operations before income taxes, and disclosure of income tax expense and cash taxes paid by jurisdiction (federal, state, and foreign). The Company adopted the new standard on October 1, 2025 and will provide the disclosures required by the standard in the fiscal 2026 Form 10-K. The adoption of the standard is not expected to have a material impact on the Company’s Consolidated Financial Statements.

In November 2023, the FASB issued a new standard, Improvement to Reportable Segment Disclosures. The new guidance enhances the disclosure of significant reportable segment expenses. The Company adopted the standard for the fiscal year ended September 30, 2025 and for interim reporting periods beginning with the quarter ended December 31, 2025. See Note L for disclosures related to the Company's reportable segments. The adoption of the standard did not have a material impact on the Company’s Consolidated Financial Statements.

Recent Tax Legislation

On July 4, 2025, the U.S. federal government enacted the One Big Beautiful Bill Act (“OBBBA”). The OBBBA contains significant changes to federal tax law, such as the permanent extension of certain expiring provisions of the Tax Cuts and Jobs Act, modifications to the international tax framework and the restoration of favorable tax treatment for certain business provisions. The provisions in the legislation are generally effective for the Company beginning in fiscal year 2026. The impact of these changes was not material to the Company’s Consolidated Financial Statements for its interim period ending March 31, 2026.

Recently Issued Accounting Standards Not Yet Adopted

In November 2024, the FASB issued a new standard, Expense Disaggregation Disclosures. The new guidance requires quantitative and qualitative disclosure of certain cost and expense categories in the notes to the financial statements for interim and annual reporting periods. The new standard is effective for the Company's fiscal 2028 annual and interim reporting periods, with early adoption permitted. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on the Company’s Consolidated Financial Statements.

In December 2025, the FASB issued amendments to the interim reporting guidance: Interim Reporting — Narrow-Scope Improvements. The guidance improves the navigability of the required interim disclosures and clarifies when that guidance is applicable. The guidance is effective for the Company's interim reporting periods beginning on October 1, 2028. The amendments

can be applied either (1) prospectively or (2) retrospectively to any or all prior periods presented in the financial statements. The Company is currently evaluating the impact of the adoption of this amendment on the Company’s Consolidated Financial Statements.

In September 2025, the FASB issued a new standard, Intangibles—Goodwill and Other—Internal-Use Software: Targeted Improvements to the Accounting for Internal-Use Software, which is intended to modernize the accounting for the costs of internal use software given the evolution of software development to the incremental and iterative development method. The amendments remove all references to prescriptive and sequential development stages and require an entity to start capitalizing software costs when management has authorized and committed to funding the software project, it is probable that the project will be completed, and the software will be used to perform the function intended. The amendments are effective for annual and interim reporting periods beginning on October 1, 2028. Early adoption is permitted as of the beginning of an annual reporting period with the amendments to be applied using a prospective, modified retrospective, or retrospective transition approach. The Company is currently evaluating the timing of adoption and the impact of the adoption of this standard on the Company’s Consolidated Financial Statements.

In December 2025, the FASB issued a new standard, Accounting for Government Grants Received by Business Entities. The standard establishes authoritative guidance on the accounting for government grants received by business entities, including guidance for a grant related to an asset and a grant related to income. The new standard allows for a number of accounting policy elections to be made upon adoption and be applied to the subsequent grants received on a prospective basis. The new standard is effective for the Company’s annual and interim reporting period beginning on October 1, 2029. The new standard provides entities with a choice of modified prospective, modified retrospective, and retrospective adoption approach. The Company is currently evaluating the impact of the adoption of this standard on its Consolidated Financial Statements.

Earnings Per Share - Calculation of Undistributed Earnings (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Earnings Per Share [Abstract]
Net income (loss) attributable to Cabot Corporation	$ 68	$ 94	$ 141	$ 187
Less: Dividends declared on common stock	24	22	48	46
Less: Dividends declared on participating securities		1		1
Undistributed earnings (loss)	44	71	93	140
Undistributed earnings (loss) allocated to common stockholders	43	70	91	138
Undistributed earnings allocated to participating security holders	$ 1	$ 1	$ 2	$ 2

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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+ Details

Acquisitions (Tables)

6 Months Ended

Mar. 31, 2026

Business Combinations [Abstract]

Summary of Provisional Estimates of the Fair Value of Assets and Liabilities Acquired


	(In millions)
Fair value of asset acquired
Cash	$	2
Accounts and notes receivable		16
Inventories		20
Other assets		12
Property, plant and equipment		34
Intangible Assets		2
Total assets acquired		86

Fair value of liabilities assumed
Accounts payable and accrued liabilities		(12	)
Other liabilities		(6	)
Total liabilities assumed		(18	)

Total identifiable net assets	$	68

Cash consideration paid	$	68

Income Tax - Effective Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Income Tax Disclosure [Abstract]
(Provision) benefit for income taxes	$ (44)	$ (49)	$ (81)	$ (90)
Effective tax rate	37.00%	32.00%	34.00%	30.00%

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

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-SubTopic 10
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-Publisher FASB
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+ Details

Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Cash Flows from Operating Activities:
Net income (loss)	$ 160	$ 209
Adjustments to reconcile net income (loss) to cash provided by operating activities:
Depreciation and amortization	90	75
Deferred tax provision (benefit)	(14)	8
Equity in earnings of affiliated companies	(3)	(4)
Share-based compensation	7	14
Other non-cash (income) expense	6	7
Cash dividends received from equity affiliates	1	12
Changes in assets and liabilities:
Accounts and notes receivable	37	(30)
Inventories		(8)
Prepaid expenses and other assets	(25)	(17)
Accounts payable and accrued liabilities	(51)	(76)
Income taxes payable	(2)
Other liabilities	(3)	7
Cash provided by (used in) operating activities	203	197
Cash Flows from Investing Activities:
Additions to property, plant and equipment	(114)	(149)
Cash paid for asset acquisition		(27)
Cash paid for acquisition of business, net of cash acquired $2	(66)
Other	2	2
Cash provided by (used in) investing activities	(178)	(174)
Cash Flows from Financing Activities:
Proceeds from short-term borrowings (original maturities greater than 90 days)	15
Repayments of short-term borrowings (original maturities greater than 90 days)	(8)
Proceeds from (repayments of) short-term borrowings, net (original maturities 90 days or less)	12
Proceeds from issuance (repayments) of commercial paper, net	142	145
Proceeds from long-term debt		6
Repayments of long-term debt	(4)	(4)
Purchases of common stock	(101)	(89)
Proceeds from sales of common stock		2
Cash dividends paid to noncontrolling interests	(47)	(20)
Cash dividends paid to common stockholders	(48)	(47)
Cash provided by (used in) financing activities	(39)	(7)
Effects of exchange rate changes on cash	8	(26)
Increase (decrease) in cash and cash equivalents	(6)	(10)
Cash and cash equivalents at beginning of period	258	223
Cash and cash equivalents at end of period	$ 252	$ 213

Financial Information by Segment - Additional Information (Detail)	6 Months Ended
	Mar. 31, 2026 Segment
Segment Reporting Information [Line Items]
Number of business reportable segments	2
Segment Reporting, CODM, Individual Title and Position or Group Name [Extensible Enumeration]	srt:ChiefExecutiveOfficerMember, srt:PresidentMember
Segment Reporting, CODM, Profit (Loss) Measure, How Used, Description	The CODM reviews Segment earnings before interest and taxes (“Segment EBIT”) at the operating segment level to allocate resources and to assess operating results and financial performance. The CODM reviews the change in the actual results compared to the same period forecast, the same period year-ago, and the preceding period on a quarterly basis.

Consolidated Statements of Operations (Unaudited) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Income Statement [Abstract]
Net sales and other operating revenues	$ 904	$ 936	$ 1,753	$ 1,891
Cost of sales	694	695	1,332	1,415
Gross profit	210	241	421	476
Selling and administrative expenses	67	64	136	130
Research and technical expenses	14	15	27	29
Income (loss) from operations	129	162	258	317
Interest and dividend income	7	7	14	13
Interest expense	(18)	(19)	(36)	(37)
Other income (expense)	2	1	2	2
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	120	151	238	295
(Provision) benefit for income taxes	(44)	(49)	(81)	(90)
Equity in earnings of affiliated companies, net of tax	2	3	3	4
Net income (loss)	78	105	160	209
Net income (loss) attributable to noncontrolling interests, net of tax	10	11	19	22
Net income (loss) attributable to Cabot Corporation	$ 68	$ 94	$ 141	$ 187
Weighted-average common shares outstanding:
Basic	52.0	54.0	52.3	54.2
Diluted	52.2	54.4	52.6	54.7
Earnings (loss) per common share:
Basic	$ 1.27	$ 1.71	$ 2.65	$ 3.4
Diluted	$ 1.27	$ 1.69	$ 2.64	$ 3.36

Restructuring - Restructuring Activities and Related Reserves (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Restructuring Cost and Reserve [Line Items]
Reserve balance	$ 8	$ 8		$ 8
Charges	8	7	$ 3	15	$ 3
Costs charged against assets	(5)	(3)
Cash paid	(2)	(4)
Reserve balance	9	8		9
Severance and Employee Benefits [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	8	7		7
Charges	3	4
Cash paid	(2)	(3)
Reserve balance	9	8		9
Non-Cash Asset Impairment and Accelerated Depreciation [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	0	0		0
Charges	5	3
Costs charged against assets	(5)	(3)
Reserve balance		0
Other [Member]
Restructuring Cost and Reserve [Line Items]
Reserve balance	$ 0	1		$ 1
Cash paid		(1)
Reserve balance		$ 0

- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References + Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Accumulated Other Comprehensive Income (Loss) ("AOCI")

6 Months Ended

Mar. 31, 2026

Stockholders' Equity Note [Abstract]

Accumulated Other Comprehensive Income (Loss) ("AOCI")

E. Accumulated Other Comprehensive Income (Loss) (“AOCI”)

Comprehensive income combines net income (loss) and other comprehensive income items, which are reported as components of stockholders’ equity in the accompanying Consolidated Balance Sheets.

Changes in each component of AOCI, net of tax, were as follows:


	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2025, attributable to Cabot Corporation	$	(316	)	$	(19	)	$	(335	)
Other comprehensive income (loss) before reclassifications		26			3			29
Amounts reclassified from AOCI		(1	)		—			(1	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3			—			3
Balance at December 31, 2025, attributable to Cabot Corporation	$	(294	)	$	(16	)	$	(310	)
Other comprehensive income (loss) before reclassifications		(6	)		—			(6	)
Amounts reclassified from AOCI		—			—			—
Less: Other comprehensive income (loss) attributable to noncontrolling interests		—			—			—
Balance at March 31, 2026, attributable to Cabot Corporation	$	(300	)	$	(16	)	$	(316	)


	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2024, attributable to Cabot Corporation	$	(342	)	$	(18	)	$	(360	)
Other comprehensive income (loss) before reclassifications		(104	)		—			(104	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(7	)		—			(7	)
Balance at December 31, 2024, attributable to Cabot Corporation	$	(439	)	$	(18	)	$	(457	)
Other comprehensive income (loss) before reclassifications		34			1			35
Amounts reclassified from AOCI		(1	)		(1	)		(2	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3			—			3
Balance at March 31, 2025, attributable to Cabot Corporation	$	(409	)	$	(18	)	$	(427	)

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations in each of the three and six months ended March 31, 2026 and 2025 are as follows:


	Affected Line Item in the Consolidated	Three Months Ended March 31						Six Months Ended March 31
	Statements of Operations	2026			2025			2026			2025
		(In millions)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense	Interest expense	$	(2	)	$	(2	)	$	(3	)	$	(3	)
(Gains) losses excluded from effectiveness testing and amortized to interest expense	Interest expense		1			—			1			1
Pension and other postretirement
Amortization of actuarial losses and prior service cost (credit)	Other income (expense)		—			(1	)		—			(1	)
Total before tax		$	(1	)	$	(3	)	$	(2	)	$	(3	)

Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Mar. 31, 2026	May 01, 2026
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2026
Document Fiscal Year Focus	2026
Document Fiscal Period Focus	Q2
Trading Symbol	CBT
Entity Registrant Name	Cabot Corporation
Entity Central Index Key	0000016040
Entity Current Reporting Status	Yes
Current Fiscal Year End Date	--09-30
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		51,621,417
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	false
Entity File Number	1-5667
Entity Tax Identification Number	04-2271897
Entity Address, Address Line One	Two Seaport Lane
Entity Address, Address Line Two	Suite 1400
Entity Address, City or Town	Boston
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02210-2019
City Area Code	617
Local Phone Number	345-0100
Security Exchange Name	NYSE
Title of 12(b) Security	Common Stock, $1 par value per share
Entity Incorporation, State or Country Code	DE
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes

Financial Information by Segment - Schedule of Details of Certain Items (Detail) - Certain Items [Member] - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Global restructuring activities	$ (8)	$ (3)	$ (15)	$ (3)
Acquisition and integration-related charges (Note C)	(1)		(1)
Legal and environmental matters and reserves		(1)		(6)
Other certain items				(1)
Total certain items	$ (9)	$ (4)	$ (16)	$ (10)

Consolidated Statements of Comprehensive Income (Loss) (Unaudited) (Parenthetical) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Statement of Comprehensive Income [Abstract]
Net of tax (provision) benefit	$ (1)	$ 3	$ (2)	$ (1)

- Definition

Amount of tax expense (benefit) allocated to other comprehensive income (loss).

+ References

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+ Details

Goodwill and Intangible Assets - Schedule of Changes in Balances (Detail) $ in Millions	6 Months Ended
	Mar. 31, 2026 USD ($)
Goodwill And Intangible Assets [Line Items]
Beginning balance	$ 134
Foreign currency impact	2
Ending balance	136
Reinforcement Materials [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	50
Ending balance	50
Performance Chemicals [Member]
Goodwill And Intangible Assets [Line Items]
Beginning balance	84
Foreign currency impact	2
Ending balance	$ 86

- Definition

Amount, after accumulated impairment loss, of asset representing future economic benefit arising from other asset acquired in business combination or from joint venture formation or both, that is not individually identified and separately recognized.

+ References

Reference 1: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Pay vs Performance Disclosure - USD ($) $ in Millions	3 Months Ended		6 Months Ended
Pay vs Performance Disclosure - USD ($) $ in Millions	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Pay vs Performance Disclosure
Net Income (Loss)	$ 68	$ 94	$ 141	$ 187

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

+ Details

Significant Accounting Policies

6 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Significant Accounting Policies

B. Significant Accounting Policies

Full details on the Company’s significant accounting policies may be obtained by referring to Note A in the 2025 10-K.

Recently Adopted Accounting Standards:

Recent Tax Legislation

Recently Issued Accounting Standards Not Yet Adopted

Restructuring

6 Months Ended

Mar. 31, 2026

Restructuring and Related Activities [Abstract]

Restructuring

I. Restructuring

2026 Restructuring

During the first quarter of fiscal 2026, the Company initiated restructuring activities in its Performance Chemicals segment ("2026 PC Plan") primarily associated with the fumed metal oxide product line. As part of the plan, the Company intends to cease production of fumed silica at its manufacturing plant in Barry, Wales in the third quarter of fiscal 2026. Cabot will continue operations to post-treat fumed silica at the site. During the three and six months ended March 31, 2026, the Company recorded charges of $6 million and $13 million, respectively, primarily related to estimated severance costs, asset impairments, and accelerated depreciation. The Company expects to record additional restructuring charges of $12 million related to this plan during the remainder of fiscal 2026 and in fiscal 2027, of which $5 million is for accelerated depreciation and $7 million is for site demolition costs. Of the total charges of $25 million related to the 2026 PC Plan, the Company expects $11 million will be cash, with $7 million of cash payments expected during fiscal 2026 and $4 million during fiscal 2027.

During the second quarter of fiscal 2026, the Reinforcement Materials segment, along with associated support functions, reorganized to better align resources with business needs. The Company recorded $2 million of severance charges associated with these actions during the quarter ended March 31, 2026 which is expected to be paid in fiscal 2026.

2025 Reorganizations

In fiscal 2025, the Company undertook various actions to enable the more efficient operation of the Company and reduce ongoing operational costs. These restructuring actions have resulted in reductions in workforce across business and functional teams. Cumulative expense recorded under the 2025 Reorganizations was $9 million through December 31, 2025, primarily related to severance costs. No additional charges have been or are expected to be recorded under this plan. The Company expects to make cash payments of $7 million related to this plan during fiscal 2026.

Details of all restructuring activities and related reserves during the three and six months ended March 31, 2026 were as follows:


	Severance and Employee Benefits			Non-Cash Asset Impairment and Accelerated Depreciation			Other			Total
	(In millions)
Reserve at September 30, 2025	$	7		$	—		$	1		$	8
Charges		4			3			—			7
Cost charged against assets		—			(3	)		—			(3	)
Cash paid		(3	)		—			(1	)		(4	)
Reserve at December 31, 2025	$	8		$	—		$	—		$	8
Charges		3			5			—			8
Cost charged against assets		—			(5	)		—			(5	)
Cash paid		(2	)		—			—			(2	)
Reserve at March 31, 2026	$	9		$	—		$	—		$	9

Cabot’s severance and employee benefits reserves are reflected in Accounts payable and accrued liabilities on the Company’s Consolidated Balance Sheets.

Cabot’s restructuring expense was recorded in the Consolidated Statement of Operations for the three and six months ended March 31, 2026 and 2025 as follows:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Cost of sales	$	7	$	2	$	13	$	2
Selling and administrative expenses		1		—		2		—
Research and technical expenses		—		1		—		1
Total	$	8	$	3	$	15	$	3

Restructuring expense is considered a Certain item, which is further discussed in Note L.

Earnings Per Share

6 Months Ended

Mar. 31, 2026

Earnings Per Share [Abstract]

Earnings Per Share

H. Earnings Per Share

The following tables summarize the components of the basic and diluted earnings (loss) per common share (“EPS”) computations:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$	68	$	94	$	141	$	187
Less: Dividends and dividend equivalents to participating securities		—		1		—		1
Less: Undistributed earnings allocated to participating securities(1)		1		1		2		2
Earnings (loss) allocated to common stockholders (numerator)	$	67	$	92	$	139	$	184

Weighted average common shares and participating securities outstanding		52.8		54.8		53.1		55.0
Less: Participating securities(1)		0.8		0.8		0.8		0.8
Adjusted weighted average common shares (denominator)		52.0		54.0		52.3		54.2

Earnings (loss) per common share - basic:	$	1.27	$	1.71	$	2.65	$	3.40

Diluted EPS:
Earnings (loss) allocated to common stockholders	$	67	$	92	$	139	$	184
Plus: Earnings allocated to participating securities		1		2		2		3
Less: Adjusted earnings allocated to participating securities(2)		1		2		2		3
Earnings (loss) allocated to common stockholders (numerator)	$	67	$	92	$	139	$	184

Adjusted weighted average common shares outstanding		52.0		54.0		52.3		54.2
Effect of dilutive securities:
Common shares issuable(3)		0.2		0.4		0.3		0.5
Adjusted weighted average common shares (denominator)		52.2		54.4		52.6		54.7

Earnings (loss) per common share - diluted:	$	1.27	$	1.69	$	2.64	$	3.36

(1)

Participating securities consist of shares underlying unvested time-based restricted stock units (the "TSUs"), earned and unvested performance-based restricted stock units (the "PSUs", and referred to in this note collectively with the TSUs as the "RSUs"), stock units accounted for under the Supplemental 401(k) Plan portion of the Company’s Deferred Compensation and Supplemental Retirement Plan, and stock units and phantom stock units accounted for under the Company’s Non-Employee Directors’ Deferral Plan. The holders of RSUs are entitled to receive dividend equivalents, payable in cash, to the extent dividends are paid on the outstanding shares of Common Stock, and equal in value to the dividends that would have been paid in respect of the Common Stock underlying the RSU. The accounts of holders of stock units and phantom stock units are credited with dividend equivalents, which are payable, in stock or cash, as the case may be, with the distribution of account balances.

Undistributed earnings are the earnings which remain after dividends declared during the period are assumed to be distributed to the common shares and participating securities. Undistributed earnings are allocated to common stockholders and participating security holders on the same basis as dividend distributions. The calculation of undistributed earnings is as follows:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Calculation of undistributed earnings (loss):
Net income (loss) attributable to Cabot Corporation	$	68	$	94	$	141	$	187
Less: Dividends declared on common stock		24		22		48		46
Less: Dividends declared on participating securities		—		1		—		1
Undistributed earnings (loss)	$	44	$	71	$	93	$	140

Allocation of undistributed earnings (loss):
Undistributed earnings (loss) allocated to common stockholders	$	43	$	70	$	91	$	138
Undistributed earnings allocated to participating security holders		1		1		2		2
Undistributed earnings (loss)	$	44	$	71	$	93	$	140

(2)

Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities.

(3)

Represents incremental shares of common stock from the assumed exercise of stock options issued under Cabot’s equity incentive plans. For the three and six months ended March 31, 2026, 593,320 and 602,401 incremental shares of common stock, respectively, were excluded from the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive. For the three and six months ended March 31, 2025, 174,689 and 86,010 incremental shares of common stock, respectively, were excluded from the calculation of diluted earnings per share because the inclusion of these shares would have been antidilutive.

Financial Information by Segment - Revenue from External Customers by Geographic Region (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 904	$ 936	$ 1,753	$ 1,891
Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	872	905	1,692	1,827
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	32	31	61	64
Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	314	335	592	669
Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	341	337	690	728
Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	217	233	410	430
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	544	594	1,064	1,205
Reinforcement Materials [Member] \| Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	219	240	416	484
Reinforcement Materials [Member] \| Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	200	213	398	460
Reinforcement Materials [Member] \| Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	125	141	250	261
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	328	311	628	622
Performance Chemicals [Member] \| Americas [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	95	95	176	185
Performance Chemicals [Member] \| Asia Pacific [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	141	124	292	268
Performance Chemicals [Member] \| Europe, Middle East and Africa [Member]
Segment Reporting Information [Line Items]
Net sales and other operating revenues	$ 92	$ 92	$ 160	$ 169

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details

Consolidated Statements of Comprehensive Income (Loss) (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Statement of Comprehensive Income [Abstract]
Net income (loss)	$ 78	$ 105	$ 160	$ 209
Other comprehensive income (loss), net of tax
Foreign currency translation adjustment, net of tax	(6)	34	20	(70)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense, net of tax	(1)	(1)	(2)	(2)
(Gains) losses excluded from effectiveness testing and amortized to interest expense, net of tax	1	0	1	1
Pension and other post-retirement benefit liability adjustments, net of tax	0	0	3	0
Other comprehensive income (loss), net of tax (provision) benefit of $(1), $3, $(2), $(1)	(6)	33	22	(71)
Comprehensive income (loss)	72	138	182	138
Net income (loss) attributable to noncontrolling interests, net of tax	10	11	19	22
Foreign currency translation adjustment attributable to noncontrolling interests, net of tax	0	3	3	(4)
Comprehensive income (loss) attributable to noncontrolling interests	10	14	22	18
Comprehensive income (loss) attributable to Cabot Corporation	$ 62	$ 124	$ 160	$ 120

Financial Information by Segment - Schedule of Reconciliation of Segment Earnings before Interest and Income Taxes to Income (Loss) before Income Taxes and Equity in Earnings of Affiliated Companies (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Interest Expense	$ (18)	$ (19)	$ (36)	$ (37)
Less: Equity in earnings of affiliated companies, net of tax	2	3	3	4
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Segment EBIT	152	181	302	356
Interest Expense	(18)	(19)	(36)	(37)
Unallocated corporate costs	(15)	(13)	(27)	(26)
General unallocated income (expense)	12	9	18	16
Less: Equity in earnings of affiliated companies, net of tax	2	3	3	4
Income from continuing operations before income taxes and equity in earnings of affiliated companies	120	151	238	295
Certain Items [Member]
Segment Reporting Information [Line Items]
Certain items	$ (9)	$ (4)	$ (16)	$ (10)

Goodwill and Intangible Assets (Tables)

6 Months Ended

Mar. 31, 2026

Goodwill and Intangible Assets Disclosure [Abstract]

Schedule of Changes in Balances

The carrying amount of goodwill attributable to each reportable segment and the changes in those balances during the six months ended March 31, 2026 are as follows:


	Reinforcement Materials		Performance Chemicals		Total
	(In millions)
Balance at September 30, 2025	$	50	$	84	$	134
Foreign currency impact		—		2		2
Balance at March 31, 2026	$	50	$	86	$	136

Schedule of Intangible Assets

The following table provides information regarding the Company’s intangible assets:


	March 31, 2026							September 30, 2025
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(In millions)
Intangible assets with finite lives
Developed technologies	$	42	$	(16	)	$	26	$	41	$	(14	)	$	27
Trademarks		2		(1	)		1		2		(1	)		1
Customer relationships		64		(38	)		26		63		(36	)		27
Total intangible assets(1)	$	108	$	(55	)	$	53	$	106	$	(51	)	$	55

(1)

Total intangible assets as of March 31, 2026 includes $2 million of intangible assets from the acquisition of MXCB.

- Definition

Tabular disclosure of goodwill by reportable segment and in total which includes a rollforward schedule.

+ References

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+ Details

Acquisitions - Summary of Provisional Estimates of the Fair Value of Assets and Liabilities Acquired (Detail) - Carbon Black Manufacturing Facility [Member] $ in Millions	Jan. 31, 2026 USD ($)
Fair value of asset acquired
Cash	$ 2
Accounts and notes receivable	16
Inventories	20
Other assets	12
Property, plant and equipment	34
Intangible Assets	2
Total assets acquired	86
Fair value of liabilities assumed
Accounts payable and accrued liabilities	(12)
Other liabilities	(6)
Total liabilities assumed	(18)
Total identifiable net assets	68
Cash consideration paid	$ 68

Subsequent Event

6 Months Ended

Mar. 31, 2026

Subsequent Events [Abstract]

Subsequent Event

M. Subsequent Events

On May 1, 2026, the Company committed to a restructuring plan to better align its carbon black production to current demand conditions. Under this restructuring plan, the Company: (i) expects to cease all operations at its plant in Campana, Argentina by the end of calendar year 2026; and (ii) subject to local works council consultations, intends to close multiple manufacturing units at its plant in Botlek, The Netherlands over the course of fiscal 2026 and 2027.

The Company expects this restructuring will result in pre-tax charges to earnings of approximately $79 million, with approximately $63 million of this amount expected to be recorded during fiscal year 2026 and $16 million during fiscal 2027. The charges primarily related to severance and employee benefit costs, accelerated depreciation, and asset impairment charges. Future cash outlays related to these actions are expected to be $24 million.

Goodwill and Intangible Assets - Schedule of Intangible Assets (Detail) - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	$ 108	$ 106
Accumulated Amortization	(55)	(51)
Net Intangible Assets, finite lives	53	55
Developed Technologies [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	42	41
Accumulated Amortization	(16)	(14)
Net Intangible Assets, finite lives	26	27
Trademarks [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	2	2
Accumulated Amortization	(1)	(1)
Net Intangible Assets, finite lives	1	1
Customer Relationships [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Value, finite lives	64	63
Accumulated Amortization	(38)	(36)
Net Intangible Assets, finite lives	$ 26	$ 27

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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+ Details

Supplier Financing Programs

6 Months Ended

Mar. 31, 2026

Payables and Accruals [Abstract]

Supplier Financing Programs

K. Supplier Financing Programs

The Company maintains supply chain finance agreements with third-party financial institutions. These agreements allow the Company’s participating suppliers to sell their receivables to such third-party financial institutions to receive payment earlier than the negotiated commercial terms between the supplier and the Company. Such sales are at the sole discretion of the supplier, and on terms and conditions that are negotiated between the supplier and the respective financial institution. The terms and conditions of the supplier invoice, including payment terms and amounts due, are not impacted by a supplier’s participation in the program. Pursuant to the supply chain finance agreements, the Company has agreed to pay financial institutions on the original due date of the applicable invoice. There are no guarantees associated with these programs. The Company's outstanding payment obligations to financial institutions related to supplier financing programs were $12 million and $13 million as of March 31, 2026 and September 30, 2025, respectively, and are included within Accounts payable and accrued liabilities on the Consolidated Balance Sheets.

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Goodwill And Intangible Assets [Line Items]
Amortization of intangible assets	$ 2	$ 2	$ 3	$ 3
Amortization expense estimated for year one			7
Amortization expense estimated for year two			7
Amortization expense estimated for year three			7
Amortization expense estimated for year four			7
Amortization expense estimated for year five			$ 7
Minimum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets			10 years
Maximum [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets			25 years
Weighted Average [Member]
Goodwill And Intangible Assets [Line Items]
Useful life of intangible assets			16 years

Financial Instruments and Fair Value Measurements - Additional Information (Detail) - USD ($)	6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Sep. 30, 2025
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Fair value, liabilities, Level 2 to Level 1 transfers, amount	$ 0	$ 0
Fair value, assets, Level 2 to Level 1 transfers, amount	0	0
Fair value, liabilities, Level 1 to Level 2 transfers, amount	0	0
Fair value, assets, Level 1 to Level 2 transfers, amount	0	0
Fair value, assets, transfers into Level 3, amount	0	0
Fair value, assets, transfers out of Level 3, amount	0	0
Fair value, liabilities, transfers into Level 3, amount	0	0
Fair value, liabilities, transfers out of Level 3, amount	0	$ 0
Fixed Rate Debt [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of long-term debt	1,090,000,000.00		$ 1,090,000,000.00
Fair value of long-term debt	1,080,000,000.00		1,090,000,000.00
Significant Observable Inputs (Level 2) [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other assets in the Consolidated Balance Sheets	9,000,000		9,000,000
Significant Observable Inputs (Level 2) [Member] \| Net Investment Hedge [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities in the Consolidated Balance Sheets	7,000,000		12,000,000
Significant Observable Inputs (Level 2) [Member] \| Forward Currency Contracts [Member] \| Maximum [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other liabilities in the Consolidated Balance Sheets	$ 1,000,000
Other assets in the Consolidated Balance Sheets			$ 1,000,000

Financial Information by Segment - Revenues From External Customers That are Categorized as Unallocated and Other (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Revenues from external customers	$ 904	$ 936	$ 1,753	$ 1,891
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	32	31	61	64
Unallocated and Other [Member] \| Shipping and Handling Fees [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 32	29	57	57
Unallocated and Other [Member] \| Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers		$ 2	$ 4	$ 7

- Definition

+ References

+ Details

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) (Parenthetical) - $ / shares	3 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Statement of Stockholders' Equity [Abstract]
Common stock, cash dividends paid, per share	$ 0.45	$ 0.45	$ 0.43	$ 0.43

Restructuring - Recorded Restructuring Expense (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Restructuring Cost and Reserve [Line Items]
Total	$ 8	$ 7	$ 3	$ 15	$ 3
Cost of Sales [Member]
Restructuring Cost and Reserve [Line Items]
Total	7		2	13	2
Selling and Administrative Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Total	$ 1			$ 2
Research and Technical Expenses [Member]
Restructuring Cost and Reserve [Line Items]
Total			$ 1		$ 1

- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References + Details

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References + Details

Accumulated Other Comprehensive Income (Loss) ("AOCI") (Tables)

6 Months Ended

Mar. 31, 2026

Equity [Abstract]

Changes in Each Component of AOCI, Net of Tax

Changes in each component of AOCI, net of tax, were as follows:


	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2025, attributable to Cabot Corporation	$	(316	)	$	(19	)	$	(335	)
Other comprehensive income (loss) before reclassifications		26			3			29
Amounts reclassified from AOCI		(1	)		—			(1	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3			—			3
Balance at December 31, 2025, attributable to Cabot Corporation	$	(294	)	$	(16	)	$	(310	)
Other comprehensive income (loss) before reclassifications		(6	)		—			(6	)
Amounts reclassified from AOCI		—			—			—
Less: Other comprehensive income (loss) attributable to noncontrolling interests		—			—			—
Balance at March 31, 2026, attributable to Cabot Corporation	$	(300	)	$	(16	)	$	(316	)


	Currency Translation Adjustment			Pension and Other Post-retirement Benefit Liability Adjustments			Total
	(In millions)
Balance at September 30, 2024, attributable to Cabot Corporation	$	(342	)	$	(18	)	$	(360	)
Other comprehensive income (loss) before reclassifications		(104	)		—			(104	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		(7	)		—			(7	)
Balance at December 31, 2024, attributable to Cabot Corporation	$	(439	)	$	(18	)	$	(457	)
Other comprehensive income (loss) before reclassifications		34			1			35
Amounts reclassified from AOCI		(1	)		(1	)		(2	)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3			—			3
Balance at March 31, 2025, attributable to Cabot Corporation	$	(409	)	$	(18	)	$	(427	)

Amounts Reclassified Out of AOCI

The amounts reclassified out of AOCI and into the Consolidated Statements of Operations in each of the three and six months ended March 31, 2026 and 2025 are as follows:


	Affected Line Item in the Consolidated	Three Months Ended March 31						Six Months Ended March 31
	Statements of Operations	2026			2025			2026			2025
		(In millions)
Derivatives: net investment hedges
(Gains) losses reclassified to interest expense	Interest expense	$	(2	)	$	(2	)	$	(3	)	$	(3	)
(Gains) losses excluded from effectiveness testing and amortized to interest expense	Interest expense		1			—			1			1
Pension and other postretirement
Amortization of actuarial losses and prior service cost (credit)	Other income (expense)		—			(1	)		—			(1	)
Total before tax		$	(1	)	$	(3	)	$	(2	)	$	(3	)

Financial Information by Segment (Tables)

6 Months Ended

Mar. 31, 2026

Segment Reporting [Abstract]

Details of Segment EBIT and Other Financial Information by Reportable Segment

Details of Segment EBIT including segment revenue and significant segment expenses regularly reviewed by the CODM are as follows:


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Three Months Ended March 31, 2026
Segment revenues from external customers	$	544		$	328		$	872
Segment cost of sales(1)		(420	)		(234	)		(654	)
Segment operating expenses(1)(2)		(32	)		(36	)		(68	)
Other Segment Items(3)		1			1			2
Segment EBIT	$	93		$	59		$	152


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Three Months Ended March 31, 2025
Segment revenues from external customers	$	594		$	311		$	905
Segment cost of sales(1)		(430	)		(229	)		(659	)
Segment operating expenses(1)(2)		(34	)		(34	)		(68	)
Other Segment Items(3)		1			2			3
Segment EBIT	$	131		$	50		$	181


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Six Months Ended March 31, 2026
Segment revenues from external customers	$	1,064		$	628		$	1,692
Segment cost of sales(1)		(802	)		(452	)		(1,254	)
Segment operating expenses(1)(2)		(68	)		(71	)		(139	)
Other Segment Items(3)		1			2			3
Segment EBIT	$	195		$	107		$	302


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Six Months Ended March 31, 2025
Segment revenues from external customers	$	1,205		$	622		$	1,827
Segment cost of sales(1)		(877	)		(459	)		(1,336	)
Segment operating expenses(1)(2)		(69	)		(70	)		(139	)
Other Segment Items(3)		2			2			4
Segment EBIT	$	261		$	95		$	356

(1)

Segment cost of sales and Segment operating expenses exclude the items described in the reconciliation of segment earnings before interest and income taxes to Income (loss) from operations before income taxes and equity in earnings of affiliated companies.

(2)

Segment operating expenses include Selling and administrative expenses and Research and technical expenses.

(3)

Other segment items include Equity in earnings of affiliated companies, net of tax.

Reconciliation of Segment earnings before interest and income taxes to Income (loss) from operations before income taxes and equity in earnings of affiliated companies is as follows:


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(In millions)
Segment EBIT	$	152		$	181		$	302		$	356
Interest Expense		(18	)		(19	)		(36	)		(37	)
Certain items (1)		(9	)		(4	)		(16	)		(10	)
Unallocated corporate costs (2)		(15	)		(13	)		(27	)		(26	)
General unallocated income (expense) (3)		12			9			18			16
Less: Equity in earnings of affiliated companies, net of tax(4)		2			3			3			4
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	$	120		$	151		$	238		$	295

(1)

Certain items are items of expense and income that management does not consider representative of the Company’s fundamental on-going segment results and they are, therefore, excluded from Segment EBIT.

Details of certain items for the three and six months ended March 31, 2026 and 2025 are as follows:


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(In millions)						(In millions)
Global restructuring activities (Note I)	$	(8	)	$	(3	)	$	(15	)	$	(3	)
Acquisition and integration-related charges (Note C)		(1	)		—			(1	)		—
Legal and environmental matters and reserves		—			(1	)		—			(6	)
Other certain items		—			—			—			(1	)
Total certain items	$	(9	)	$	(4	)	$	(16	)	$	(10	)

(2)

Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

(3)

General unallocated income (expense) consists of gains (losses) arising from foreign currency transactions, net of other foreign currency risk management activities, interest and dividend income, the profit or loss related to the corporate adjustment for unearned revenue, and unrealized holding gains (losses) for investments. This does not include items of income or expense that are separately treated as Certain items.

(4)

Equity in earnings of affiliated companies, net of tax is included in Segment EBIT and is removed to reconcile to Income (loss) from operations before taxes and equity in earnings of affiliated companies.

Financial information by reportable segment is as follows:


	Reinforcement Materials		Performance Chemicals		Segment Total		Unallocated and Other		Consolidated Total
	(In millions)
Three Months Ended March 31, 2026
Revenues from external customers(1)	$	544	$	328	$	872	$	32	$	904

Three Months Ended March 31, 2025
Revenues from external customers(1)	$	594	$	311	$	905	$	31	$	936

Six Months Ended March 31, 2026
Revenues from external customers(2)	$	1,064	$	628	$	1,692	$	61	$	1,753

Six Months Ended March 31, 2025
Revenues from external customers(2)	$	1,205	$	622	$	1,827	$	64	$	1,891

(1)

Consolidated Total Revenues from external customers reconciles to Net sales and other operating revenues on the Consolidated Statements of Operations. Revenues from external customers that are categorized as Unallocated and Other are summarized as follows:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Shipping and handling fees	$	32	$	29	$	57	$	57
Other		—		2		4		7
Total	$	32	$	31	$	61	$	64

Revenues from External Customers by Geographic Region

The Company’s segments operate globally. In addition to presenting Revenue from external customers by reportable segment, the following tables further disaggregate Revenues from external customers by geographic region.


	Three Months Ended March 31, 2026
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	219	$	95	$	314
Asia Pacific		200		141		341
Europe, Middle East and Africa		125		92		217
Segment revenues from external customers		544		328		872
Unallocated and other						32
Net sales and other operating revenues					$	904


	Three Months Ended March 31, 2025
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	240	$	95	$	335
Asia Pacific		213		124		337
Europe, Middle East and Africa		141		92		233
Segment revenues from external customers		594		311		905
Unallocated and other						31
Net sales and other operating revenues					$	936


	Six Months Ended March 31, 2026
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	416	$	176	$	592
Asia Pacific		398		292		690
Europe, Middle East and Africa		250		160		410
Segment revenues from external customers		1,064		628		1,692
Unallocated and other						61
Net sales and other operating revenues					$	1,753


	Six Months Ended March 31, 2025
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	484	$	185	$	669
Asia Pacific		460		268		728
Europe, Middle East and Africa		261		169		430
Segment revenues from external customers		1,205		622		1,827
Unallocated and other						64
Net sales and other operating revenues					$	1,891

Earnings Per Share - Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS) (Detail) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$ 68	$ 94	$ 141	$ 187
Less: Dividends and dividend equivalents to participating securities		1		1
Less: Undistributed earnings allocated to participating securities	1	1	2	2
Earnings (loss) allocated to common stockholders (numerator)	$ 67	$ 92	$ 139	$ 184
Weighted average common shares and participating securities outstanding	52.8	54.8	53.1	55.0
Less: Participating securities	0.8	0.8	0.8	0.8
Adjusted weighted average common shares (denominator)	52.0	54.0	52.3	54.2
Earnings (loss) per common share - basic:	$ 1.27	$ 1.71	$ 2.65	$ 3.4
Diluted EPS:
Earnings (loss) allocated to common stockholders	$ 67	$ 92	$ 139	$ 184
Plus: Earnings allocated to participating securities	1	2	2	3
Less: Adjusted earnings allocated to participating securities	1	2	2	3
Earnings (loss) allocated to common stockholders (numerator)	$ 67	$ 92	$ 139	$ 184
Adjusted weighted average common shares outstanding	52.0	54.0	52.3	54.2
Common shares issuable	0.2	0.4	0.3	0.5
Adjusted weighted average common shares (denominator)	52.2	54.4	52.6	54.7
Earnings (loss) per common share - diluted:	$ 1.27	$ 1.69	$ 2.64	$ 3.36

Accumulated Other Comprehensive Income (Loss) ("AOCI") - Amounts Reclassified Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ (1)	$ (3)	$ (2)	$ (3)
(Gains) Losses Reclassified to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	(2)	(2)	(3)	(3)
(Gains) Losses Excluded from Effectiveness Testing and Amortized to Interest Expense [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax	$ 1		$ 1	1
Amortization of Actuarial Losses and Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax		$ (1)		$ (1)

Insider Trading Arrangements	3 Months Ended
Insider Trading Arrangements	Mar. 31, 2026
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false
Rule 10b5-1 Arrangement Modified	false
Non-Rule 10b5-1 Arrangement Modified	false

Goodwill and Intangible Assets

6 Months Ended

Mar. 31, 2026

Goodwill and Intangible Assets Disclosure [Abstract]

Goodwill and Intangible Assets

D. Goodwill and Intangible Assets

The carrying amount of goodwill attributable to each reportable segment and the changes in those balances during the six months ended March 31, 2026 are as follows:


	Reinforcement Materials		Performance Chemicals		Total
	(In millions)
Balance at September 30, 2025	$	50	$	84	$	134
Foreign currency impact		—		2		2
Balance at March 31, 2026	$	50	$	86	$	136

The following table provides information regarding the Company’s intangible assets:


	March 31, 2026							September 30, 2025
	Gross Carrying Value		Accumulated Amortization			Net Intangible Assets		Gross Carrying Value		Accumulated Amortization			Net Intangible Assets
	(In millions)
Intangible assets with finite lives
Developed technologies	$	42	$	(16	)	$	26	$	41	$	(14	)	$	27
Trademarks		2		(1	)		1		2		(1	)		1
Customer relationships		64		(38	)		26		63		(36	)		27
Total intangible assets(1)	$	108	$	(55	)	$	53	$	106	$	(51	)	$	55

(1)

Total intangible assets as of March 31, 2026 includes $2 million of intangible assets from the acquisition of MXCB.

Intangible assets are amortized over their estimated useful lives, which range between ten and twenty-five years, with a weighted average amortization period of approximately sixteen years. Amortization expense was $2 million for both the three months ended March 31, 2026 and 2025. Amortization expense was $3 million for both the six months ended March 31, 2026 and 2025. Amortization expense is included in Cost of sales, Selling and administrative expenses and Research and technical expenses in the Consolidated Statements of Operations. Total amortization expense is estimated to be approximately $7 million each year for the next five fiscal years.

Consolidated Balance Sheets (Parenthetical) (Unaudited) - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Statement of Financial Position [Abstract]
Accounts and notes receivable, reserve for doubtful accounts	$ 5	$ 5
Preferred stock, authorized shares	2,000,000	2,000,000
Preferred stock, par value	$ 1	$ 1
Preferred stock, Issued shares	0	0
Preferred stock, Outstanding shares	0	0
Common stock, authorized shares	200,000,000	200,000,000
Common stock, par value	$ 1	$ 1
Common stock, issued shares	51,694,096	52,962,353
Common stock, outstanding shares	51,579,624	52,842,481
Common treasury stock, shares	115,063	119,872

Consolidated Statements of Cash Flows (Unaudited) (Parenthetical) - USD ($) $ in Millions	6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Statement of Cash Flows [Abstract]
Cash acquired in acquisition of business	$ 2	$ 2

Goodwill and Intangible Assets - Schedule of Intangible Assets (Parenthetical) (Detail) $ in Millions	6 Months Ended
	Mar. 31, 2026 USD ($)
Finite-Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 2

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

+ Details

Acquisitions

6 Months Ended

Mar. 31, 2026

Business Combinations [Abstract]

Acquisitions

C. Acquisitions

Business acquisition

On January 31, 2026, the Company purchased 100% of the registered capital of Mexico Carbon Manufacturing, S.A. de C.V. (“MXCB”), a carbon black manufacturing facility in Tamaulipas, Mexico, for a purchase price of $68 million, which included $2 million of cash acquired. The Company incurred acquisition and integration costs of $1 million through March 31, 2026 associated with the transaction, which are included in Selling and administrative expenses in the Consolidated Statements of Operations.

The operating results of MXCB were included in the results of the Company’s Reinforcement Materials segment beginning in the second quarter of 2026, including approximately $12 million of revenue in the quarter.

The provisional estimates of the fair value of assets and liabilities acquired as of January 31, 2026 are set forth below based on the cash consideration.


	(In millions)
Fair value of asset acquired
Cash	$	2
Accounts and notes receivable		16
Inventories		20
Other assets		12
Property, plant and equipment		34
Intangible Assets		2
Total assets acquired		86

Fair value of liabilities assumed
Accounts payable and accrued liabilities		(12	)
Other liabilities		(6	)
Total liabilities assumed		(18	)

Total identifiable net assets	$	68

Cash consideration paid	$	68

Asset acquisition

In October 2024, the Company completed the purchase of certain assets and licensed related technology, which the Company uses to manufacture products for its battery materials product line. The Company paid $27 million, which was allocated to the identifiable assets on a relative fair value basis, with $19 million allocated to property, plant and equipment and $8 million to intangible assets.

- Definition

The entire disclosure for business combination.

+ References

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+ Details

Financial Information by Segment

6 Months Ended

Mar. 31, 2026

Segment Reporting [Abstract]

Financial Information by Segment

L. Financial Information by Segment

Segment Information

The Company identifies a product line as an operating segment if: i) it engages in business activities from which it may earn revenues and incur expenses; ii) its operating results are regularly reviewed by the Chief Operating Decision Maker (“CODM”), who is Cabot’s President and Chief Executive Officer, to make decisions about resources to be allocated to the segment and assess its performance; and iii) it has available discrete financial information.

Operating segments are aggregated into a reportable segment if the operating segments are determined to have similar economic characteristics and if the operating segments are similar in the following areas: i) nature of products and services; ii) nature of production processes; iii) type or class of customer for their products and services; iv) methods used to distribute the products or provide services; and v) if applicable, the nature of the regulatory environment. The Company has two reportable segments: Reinforcement Materials and Performance Chemicals. The Performance Chemicals reporting segment aggregates the specialty carbons, specialty compounds, fumed metal oxides, battery materials, inkjet colorants and aerogel product lines.

The CODM reviews Segment earnings before interest and taxes (“Segment EBIT”) at the operating segment level to allocate resources and to assess operating results and financial performance. The CODM reviews the change in the actual results compared to the same period forecast, the same period year-ago, and the preceding period on a quarterly basis. Segment EBIT includes all items that are controlled by the business segment and those management considers are representative of the fundamental on-going segment results.

Details of Segment EBIT including segment revenue and significant segment expenses regularly reviewed by the CODM are as follows:


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Three Months Ended March 31, 2026
Segment revenues from external customers	$	544		$	328		$	872
Segment cost of sales(1)		(420	)		(234	)		(654	)
Segment operating expenses(1)(2)		(32	)		(36	)		(68	)
Other Segment Items(3)		1			1			2
Segment EBIT	$	93		$	59		$	152


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Three Months Ended March 31, 2025
Segment revenues from external customers	$	594		$	311		$	905
Segment cost of sales(1)		(430	)		(229	)		(659	)
Segment operating expenses(1)(2)		(34	)		(34	)		(68	)
Other Segment Items(3)		1			2			3
Segment EBIT	$	131		$	50		$	181


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Six Months Ended March 31, 2026
Segment revenues from external customers	$	1,064		$	628		$	1,692
Segment cost of sales(1)		(802	)		(452	)		(1,254	)
Segment operating expenses(1)(2)		(68	)		(71	)		(139	)
Other Segment Items(3)		1			2			3
Segment EBIT	$	195		$	107		$	302


	Reinforcement Materials			Performance Chemicals			Segment Total
	(In millions)
Six Months Ended March 31, 2025
Segment revenues from external customers	$	1,205		$	622		$	1,827
Segment cost of sales(1)		(877	)		(459	)		(1,336	)
Segment operating expenses(1)(2)		(69	)		(70	)		(139	)
Other Segment Items(3)		2			2			4
Segment EBIT	$	261		$	95		$	356

(1)

(2)

Segment operating expenses include Selling and administrative expenses and Research and technical expenses.

(3)

Other segment items include Equity in earnings of affiliated companies, net of tax.

Reconciliation of Segment earnings before interest and income taxes to Income (loss) from operations before income taxes and equity in earnings of affiliated companies is as follows:


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(In millions)
Segment EBIT	$	152		$	181		$	302		$	356
Interest Expense		(18	)		(19	)		(36	)		(37	)
Certain items (1)		(9	)		(4	)		(16	)		(10	)
Unallocated corporate costs (2)		(15	)		(13	)		(27	)		(26	)
General unallocated income (expense) (3)		12			9			18			16
Less: Equity in earnings of affiliated companies, net of tax(4)		2			3			3			4
Income (loss) from operations before income taxes and equity in earnings of affiliated companies	$	120		$	151		$	238		$	295

(1)

Details of certain items for the three and six months ended March 31, 2026 and 2025 are as follows:


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(In millions)						(In millions)
Global restructuring activities (Note I)	$	(8	)	$	(3	)	$	(15	)	$	(3	)
Acquisition and integration-related charges (Note C)		(1	)		—			(1	)		—
Legal and environmental matters and reserves		—			(1	)		—			(6	)
Other certain items		—			—			—			(1	)
Total certain items	$	(9	)	$	(4	)	$	(16	)	$	(10	)

(2)

Unallocated corporate costs are not controlled by the segments and primarily benefit corporate interests.

(3)

(4)

Financial information by reportable segment is as follows:


	Reinforcement Materials		Performance Chemicals		Segment Total		Unallocated and Other		Consolidated Total
	(In millions)
Three Months Ended March 31, 2026
Revenues from external customers(1)	$	544	$	328	$	872	$	32	$	904

Three Months Ended March 31, 2025
Revenues from external customers(1)	$	594	$	311	$	905	$	31	$	936

Six Months Ended March 31, 2026
Revenues from external customers(2)	$	1,064	$	628	$	1,692	$	61	$	1,753

Six Months Ended March 31, 2025
Revenues from external customers(2)	$	1,205	$	622	$	1,827	$	64	$	1,891

(1)


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Shipping and handling fees	$	32	$	29	$	57	$	57
Other		—		2		4		7
Total	$	32	$	31	$	61	$	64

Geographic Information


	Three Months Ended March 31, 2026
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	219	$	95	$	314
Asia Pacific		200		141		341
Europe, Middle East and Africa		125		92		217
Segment revenues from external customers		544		328		872
Unallocated and other						32
Net sales and other operating revenues					$	904


	Three Months Ended March 31, 2025
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	240	$	95	$	335
Asia Pacific		213		124		337
Europe, Middle East and Africa		141		92		233
Segment revenues from external customers		594		311		905
Unallocated and other						31
Net sales and other operating revenues					$	936


	Six Months Ended March 31, 2026
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	416	$	176	$	592
Asia Pacific		398		292		690
Europe, Middle East and Africa		250		160		410
Segment revenues from external customers		1,064		628		1,692
Unallocated and other						61
Net sales and other operating revenues					$	1,753


	Six Months Ended March 31, 2025
	Reinforcement Materials		Performance Chemicals		Consolidated Total
	(In millions)
Americas	$	484	$	185	$	669
Asia Pacific		460		268		728
Europe, Middle East and Africa		261		169		430
Segment revenues from external customers		1,205		622		1,827
Unallocated and other						64
Net sales and other operating revenues					$	1,891

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 280
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 21
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+ Details

Income Tax (Tables)

6 Months Ended

Mar. 31, 2026

Income Tax Disclosure [Abstract]

Effective Tax Rate


	Three Months Ended March 31						Six Months Ended March 31
	2026			2025			2026			2025
	(Dollars in millions)
(Provision) benefit for income taxes	$	(44	)	$	(49	)	$	(81	)	$	(90	)
Effective tax rate		37	%		32	%		34	%		30	%

Financial Information by Segment - Financial Information by Reportable Segment (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Revenues from external customers	$ 904	$ 936	$ 1,753	$ 1,891
Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	872	905	1,692	1,827
Unallocated and Other [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	32	31	61	64
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	544	594	1,064	1,205
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenues from external customers	$ 328	$ 311	$ 628	$ 622

- Definition

+ References

+ Details

Subsequent Event - Additional Information (Detail) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
	May 01, 2026	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2026
Subsequent Event [Line Items]
Cash payment for restructuring		$ 2	$ 4
Fiscal 2026 [Member]
Subsequent Event [Line Items]
Expected restructuring charge				$ 63
Fiscal 2027 [Member]
Subsequent Event [Line Items]
Expected restructuring charge				$ 16
Subsequent Event [Member]
Subsequent Event [Line Items]
Pre tax charges to earnings	$ 79
Cash payment for restructuring	$ 24

Financial Instruments and Fair Value Measurements

6 Months Ended

Mar. 31, 2026

Fair Value Disclosures [Abstract]

Financial Instruments and Fair Value Measurements

J. Financial Instruments and Fair Value Measurements

The FASB authoritative guidance on fair value measurements defines fair value, provides a framework for measuring fair value, and requires certain disclosures about fair value measurements. The required disclosures focus on the inputs used to measure fair value. The guidance establishes the following hierarchy for categorizing these inputs:


Level 1	—	Quoted market prices in active markets for identical assets or liabilities

Level 2	—	Significant other observable inputs (e.g., quoted prices for similar items in active markets, quoted prices for identical or similar items in markets that are not active, inputs other than quoted prices that are observable such as interest rate and yield curves, and market-corroborated inputs)

Level 3	—	Significant unobservable inputs

There were no transfers of financial assets or liabilities measured at fair value between Level 1 and Level 2 and there were no Level 3 investments during the first six months of either fiscal 2026 or 2025.

At March 31, 2026 and September 30, 2025, the fair values of cash and cash equivalents, accounts and notes receivable, accounts payable and accrued liabilities, and short-term borrowings and short-term variable rate debt approximated their carrying values due to the short-term nature of these instruments. Cash and cash equivalents are classified as Level 1 within the fair value hierarchy.

At March 31, 2026 and September 30, 2025, Cabot had derivatives relating to foreign currency risks, including a net investment hedge and forward foreign currency contracts, carried at fair value. At March 31, 2026, the fair value of the net investment hedge was a net liability of $7 million and was included in Prepaid expenses and other current assets and Accounts payable and accrued liabilities on the Consolidated Balance Sheet. At September 30, 2025, the fair value of the net investment hedge was a net liability of $12 million and was included in Prepaid expenses and other current assets and Other liabilities on the Consolidated Balance Sheet. As of March 31, 2026 and September 30, 2025, the fair value of the forward currency contracts was a net liability of less than $1 million and a net asset of less than $1 million, respectively, and was included in Prepaid expenses and other current assets and Accounts payable and accrued liabilities on the Consolidated Balance Sheets. These derivatives are classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on observable inputs.

At both March 31, 2026 and September 30, 2025, the fair value of guaranteed investment contracts included in Other assets on the Consolidated Balance Sheets was $9 million. Guaranteed investment contracts were classified as Level 2 instruments within the fair value hierarchy as the fair value determination was based on observable inputs.

The carrying value of the long-term fixed rate debt was $1.09 billion as of both March 31, 2026 and September 30, 2025. The fair value of the long-term fixed rate debt was $1.08 billion and $1.09 billion, respectively, as of March 31, 2026 and September 30, 2025. The fair values of Cabot’s fixed rate long-term debt are estimated based on comparable quoted market prices at the respective period ends. The carrying amounts of Cabot’s floating rate long-term debt and finance and operating lease obligations approximate their fair values. All such measurements are based on observable inputs and are classified as Level 2 within the fair value hierarchy.

Earnings Per Share - Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS) (Parenthetical) (Detail) - shares	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Earnings Per Share [Abstract]
Antidilutive securities excluded from computation of earnings per share	593,320	174,689	602,401	86,010

Financial Information by Segment - Schedule of Details of Segment EBIT Including Segment Revenue and Significant Segment Expenses (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Segment Reporting Information [Line Items]
Segment revenues from external customers	$ 904	$ 936	$ 1,753	$ 1,891
Segment cost of sales	694	695	1,332	1,415
Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment revenues from external customers	872	905	1,692	1,827
Segment cost of sales	(654)	(659)	(1,254)	(1,336)
Segment operating expenses	(68)	(68)	(139)	(139)
Other Segment Items	2	3	3	4
Segment EBIT	152	181	302	356
Reinforcement Materials [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment revenues from external customers	544	594	1,064	1,205
Segment cost of sales	(420)	(430)	(802)	(877)
Segment operating expenses	(32)	(34)	(68)	(69)
Other Segment Items	1	1	1	2
Segment EBIT	93	131	195	261
Performance Chemicals [Member] \| Operating Segments [Member]
Segment Reporting Information [Line Items]
Segment revenues from external customers	328	311	628	622
Segment cost of sales	(234)	(229)	(452)	(459)
Segment operating expenses	(36)	(34)	(71)	(70)
Other Segment Items	1	2	2	2
Segment EBIT	$ 59	$ 50	$ 107	$ 95

- Definition

The aggregate costs related to goods produced and sold and services rendered by an entity during the reporting period. This excludes costs incurred during the reporting period related to financial services rendered and other revenue generating activities.

+ References + Details

- Definition

+ References

+ Details

Earnings Per Share (Tables)

6 Months Ended

Mar. 31, 2026

Earnings Per Share [Abstract]

Components of Basic and Diluted Earnings (Loss) Per Common Share (EPS)

The following tables summarize the components of the basic and diluted earnings (loss) per common share (“EPS”) computations:


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions, except per share amounts)
Basic EPS:
Net income (loss) attributable to Cabot Corporation	$	68	$	94	$	141	$	187
Less: Dividends and dividend equivalents to participating securities		—		1		—		1
Less: Undistributed earnings allocated to participating securities(1)		1		1		2		2
Earnings (loss) allocated to common stockholders (numerator)	$	67	$	92	$	139	$	184

Weighted average common shares and participating securities outstanding		52.8		54.8		53.1		55.0
Less: Participating securities(1)		0.8		0.8		0.8		0.8
Adjusted weighted average common shares (denominator)		52.0		54.0		52.3		54.2

Earnings (loss) per common share - basic:	$	1.27	$	1.71	$	2.65	$	3.40

Diluted EPS:
Earnings (loss) allocated to common stockholders	$	67	$	92	$	139	$	184
Plus: Earnings allocated to participating securities		1		2		2		3
Less: Adjusted earnings allocated to participating securities(2)		1		2		2		3
Earnings (loss) allocated to common stockholders (numerator)	$	67	$	92	$	139	$	184

Adjusted weighted average common shares outstanding		52.0		54.0		52.3		54.2
Effect of dilutive securities:
Common shares issuable(3)		0.2		0.4		0.3		0.5
Adjusted weighted average common shares (denominator)		52.2		54.4		52.6		54.7

Earnings (loss) per common share - diluted:	$	1.27	$	1.69	$	2.64	$	3.36

(1)

Calculation of Undistributed Earnings


	Three Months Ended March 31				Six Months Ended March 31
	2026		2025		2026		2025
	(In millions)
Calculation of undistributed earnings (loss):
Net income (loss) attributable to Cabot Corporation	$	68	$	94	$	141	$	187
Less: Dividends declared on common stock		24		22		48		46
Less: Dividends declared on participating securities		—		1		—		1
Undistributed earnings (loss)	$	44	$	71	$	93	$	140

Allocation of undistributed earnings (loss):
Undistributed earnings (loss) allocated to common stockholders	$	43	$	70	$	91	$	138
Undistributed earnings allocated to participating security holders		1		1		2		2
Undistributed earnings (loss)	$	44	$	71	$	93	$	140

(2)

Undistributed earnings are adjusted for the assumed distribution of dividends to the dilutive securities, which are described in (3) below, and then reallocated to participating securities.

(3)

Consolidated Balance Sheets (Unaudited) - USD ($) $ in Millions	Mar. 31, 2026	Sep. 30, 2025
Current assets:
Cash and cash equivalents	$ 252	$ 258
Accounts and notes receivable, net of reserve for doubtful accounts of $5 and $5	657	671
Inventories:
Raw materials	144	134
Finished goods	310	303
Other	68	67
Total inventories	522	504
Prepaid expenses and other current assets	116	106
Total current assets	1,547	1,539
Property, plant and equipment	4,514	4,405
Accumulated depreciation	(2,763)	(2,694)
Net property, plant and equipment	1,751	1,711
Goodwill	136	134
Equity affiliates	18	16
Intangible assets, net	53	55
Deferred income taxes	198	180
Other assets	194	180
Total assets	3,897	3,815
Current liabilities:
Short-term borrowings	175	14
Accounts payable and accrued liabilities	598	648
Income taxes payable	34	35
Current portion of long-term debt	261	260
Total current liabilities	1,068	957
Long-term debt	863	856
Deferred income taxes	40	39
Other liabilities	239	258
Contingencies (Note F)
Preferred stock:
Authorized: 2,000,000 shares of $1 par value, Issued and Outstanding: None and none
Common stock:
Authorized: 200,000,000 shares of $1 par value, Issued: 51,694,096 and 52,962,353 shares, Outstanding: 51,579,624 and 52,842,481 shares	52	53
Less cost of 115,063 and 119,872 shares of common treasury stock	(3)	(3)
Retained earnings	1,835	1,835
Accumulated other comprehensive income (loss)	(316)	(335)
Total Cabot Corporation stockholders' equity	1,568	1,550
Noncontrolling interests	119	155
Total stockholders' equity	1,687	1,705
Total liabilities and stockholders' equity	$ 3,897	$ 3,815

Restructuring - Additional Information (Details) - USD ($)	3 Months Ended			6 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Restructuring Cost and Reserve [Line Items]
Severance costs	$ 2,000,000
Total charges	8,000,000	$ 7,000,000	$ 3,000,000	$ 15,000,000	$ 3,000,000
Cash payment for restructuring	2,000,000	4,000,000
2026 PC Plan [Member]
Restructuring Cost and Reserve [Line Items]
Estimated severance costs and asset impairments	$ 6,000,000			13,000,000
Total charges				25,000,000
Cash payment for restructuring				11,000,000
2026 PC Plan [Member] \| Remainder of Fiscal 2026 [Member]
Restructuring Cost and Reserve [Line Items]
Expected additional restructuring charges				12,000,000
Cash payment for restructuring				7,000,000
2026 PC Plan [Member] \| Fiscal 2027 [Member]
Restructuring Cost and Reserve [Line Items]
Expected additional restructuring charges				12,000,000
Cash payment for restructuring				4,000,000
2026 PC Plan [Member] \| Accelerated Depreciation [Member]
Restructuring Cost and Reserve [Line Items]
Expected additional restructuring charges				5,000,000
2026 PC Plan [Member] \| Site Demolition Costs [Member]
Restructuring Cost and Reserve [Line Items]
Expected additional restructuring charges				7,000,000
2025 Reorganizations [Member]
Restructuring Cost and Reserve [Line Items]
Severance costs		$ 9,000,000
Additional restructuring charges				0
2025 Reorganizations [Member] \| Remainder of Fiscal 2026 [Member]
Restructuring Cost and Reserve [Line Items]
Cash payment for restructuring				$ 7,000,000

Accumulated Other Comprehensive Income (Loss) ("AOCI") - Changes in Each Component of AOCI, Net of Tax (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Dec. 31, 2025	Mar. 31, 2025	Dec. 31, 2024
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	$ 1,729	$ 1,705	$ 1,515	$ 1,590
Ending Balance	1,687	1,729	1,590	1,515
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(294)	(316)	(439)	(342)
Other comprehensive income (loss) before reclassifications	(6)	26	34	(104)
Amounts reclassified from AOCI	(0)	(1)	(1)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3	3	(7)
Ending Balance	(300)	(294)	(409)	(439)
Pension and Other Post-retirement Benefit Liability Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(16)	(19)	(18)	(18)
Other comprehensive income (loss) before reclassifications		3	1
Amounts reclassified from AOCI			(1)
Ending Balance	(16)	(16)	(18)	(18)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Beginning Balance	(310)	(335)	(457)	(360)
Other comprehensive income (loss) before reclassifications	(6)	29	35	(104)
Amounts reclassified from AOCI	(0)	(1)	(2)
Less: Other comprehensive income (loss) attributable to noncontrolling interests		3	3	(7)
Ending Balance	$ (316)	$ (310)	$ (427)	$ (457)

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 815
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+ Details

- Definition

Amount after tax, before reclassification adjustments of other comprehensive income (loss).

+ References

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Amount after tax of reclassification adjustments of other comprehensive income (loss).

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Amount of equity (deficit) attributable to parent and noncontrolling interest. Excludes temporary equity.

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+ Details

Basis of Presentation

6 Months Ended

Mar. 31, 2026

Accounting Policies [Abstract]

Basis of Presentation

A. Basis of Presentation

The consolidated financial statements have been prepared in conformity with accounting principles generally accepted in the United States (“U.S.”) (“GAAP”) and include the accounts of Cabot Corporation (“Cabot” or the “Company”) and its wholly-owned subsidiaries and majority-owned and controlled U.S. and non-U.S. subsidiaries. Additionally, Cabot considers consolidation of entities over which control is achieved through means other than voting rights. Intercompany transactions have been eliminated in consolidation.

The consolidated financial statements have been prepared in accordance with the requirements of Form 10-Q and consequently do not include all disclosures required by Form 10-K. Additional information may be obtained by referring to Cabot’s Annual Report on Form 10-K for its fiscal year ended September 30, 2025 (the “2025 10-K”).

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenues and expenses during the reporting period. Actual results could differ from those estimates.

The financial information submitted herewith is unaudited and reflects all adjustments which are, in the opinion of management, necessary to provide a fair statement of the results for the interim periods ended March 31, 2026 and 2025. All such adjustments are of a normal recurring nature. The results for interim periods are not necessarily indicative of the results expected for the fiscal year.

Consolidated Statements of Changes in Stockholders' Equity (Unaudited) - USD ($) shares in Thousands, $ in Millions	Total	Common Stock, Net of Treasury Stock [Member]	Additional Paid-in Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Total Cabot Corporation Stockholders' Equity [Member]	Noncontrolling Interests [Member]
Beginning Balance at Sep. 30, 2024	$ 1,590	$ 51		$ 1,734	$ (360)	$ 1,425	$ 165
Beginning Balance, Shares at Sep. 30, 2024		54,297
Net income (loss)	104			93		93	11
Total other comprehensive income (loss), net of tax	(104)				(97)	(97)	(7)
Cash dividends paid on common stock	(24)			(24)		(24)
Cash dividends declared to noncontrolling interests	(20)						(20)
Issuance of stock under equity compensation plans	2		$ 2			2
Issuance of stock under equity compensation plans, Shares		308
Share-based compensation	8		8			8
Purchase and retirement of common stock	(41)		(10)	(31)		(41)
Purchase and retirement of common stock, Shares		(390)
Ending Balance at Dec. 31, 2024	1,515	$ 51		1,772	(457)	1,366	149
Ending Balance, Shares at Dec. 31, 2024		54,215
Beginning Balance at Sep. 30, 2024	1,590	$ 51		1,734	(360)	1,425	165
Beginning Balance, Shares at Sep. 30, 2024		54,297
Net income (loss)	209
Total other comprehensive income (loss), net of tax	(71)
Ending Balance at Mar. 31, 2025	1,590	$ 51		1,803	(427)	1,427	163
Ending Balance, Shares at Mar. 31, 2025		53,701
Beginning Balance at Dec. 31, 2024	1,515	$ 51		1,772	(457)	1,366	149
Beginning Balance, Shares at Dec. 31, 2024		54,215
Net income (loss)	105			94		94	11
Total other comprehensive income (loss), net of tax	33				30	30	3
Cash dividends paid on common stock	(23)			(23)		(23)
Issuance of stock under equity compensation plans, Shares		16
Share-based compensation	6		6			6
Purchase and retirement of common stock	(46)		(6)	(40)		(46)
Purchase and retirement of common stock, Shares		(530)
Ending Balance at Mar. 31, 2025	1,590	$ 51		1,803	(427)	1,427	163
Ending Balance, Shares at Mar. 31, 2025		53,701
Beginning Balance at Sep. 30, 2025	1,705	$ 50		1,835	(335)	1,550	155
Beginning Balance, Shares at Sep. 30, 2025		52,842
Net income (loss)	82			73		73	9
Total other comprehensive income (loss), net of tax	28				25	25	3
Cash dividends paid on common stock	(24)			(24)		(24)
Cash dividends declared to noncontrolling interests	(13)						(13)
Issuance of stock under equity compensation plans, Shares		170
Share-based compensation	3		3			3
Purchase and retirement of common stock	(52)	$ (1)	(3)	(48)		(52)
Purchase and retirement of common stock, Shares		(796)
Ending Balance at Dec. 31, 2025	1,729	$ 49		1,836	(310)	1,575	154
Ending Balance, Shares at Dec. 31, 2025		52,216
Beginning Balance at Sep. 30, 2025	1,705	$ 50		1,835	(335)	1,550	155
Beginning Balance, Shares at Sep. 30, 2025		52,842
Net income (loss)	160
Total other comprehensive income (loss), net of tax	22
Ending Balance at Mar. 31, 2026	1,687	$ 49		1,835	(316)	1,568	119
Ending Balance, Shares at Mar. 31, 2026		51,580
Beginning Balance at Dec. 31, 2025	1,729	$ 49		1,836	(310)	1,575	154
Beginning Balance, Shares at Dec. 31, 2025		52,216
Net income (loss)	78			68		68	10
Total other comprehensive income (loss), net of tax	(6)				(6)	(6)
Cash dividends paid on common stock	(24)			(24)		(24)
Cash dividends declared to noncontrolling interests	(45)						(45)
Issuance of stock under equity compensation plans, Shares		15
Share-based compensation	4		4			4
Purchase and retirement of common stock	(49)		$ (4)	(45)		(49)
Purchase and retirement of common stock, Shares		(651)
Ending Balance at Mar. 31, 2026	$ 1,687	$ 49		$ 1,835	$ (316)	$ 1,568	$ 119
Ending Balance, Shares at Mar. 31, 2026		51,580

Acquisitions - Additional Information (Detail) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		6 Months Ended
	Jan. 31, 2026	Oct. 31, 2024	Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2026	Mar. 31, 2025
Business Acquisition [Line Items]
Businesses acquisition, net of cash acquired					$ 66
Segment revenues from external customers			$ 904	$ 936	1,753	$ 1,891
Carbon Black Manufacturing Facility [Member]
Business Acquisition [Line Items]
Business combination, voting equity interest acquired, percentage	100.00%
Business acquisition, purchase price allocated to identifiable assets on relative fair value basis	$ 68
Business acquisition, purchase price allocation, property, plants and equipment	34
Business acquisition, cash consideration	68
Businesses acquisition, net of cash acquired	$ 2
Business combination, effective date of acquisition	Jan. 31, 2026
Acquisition and integration costs incurred					$ 1
Segment revenues from external customers			$ 12
Certain Assets and Licensed Related Technology [Member]
Business Acquisition [Line Items]
Business acquisition, purchase price allocated to identifiable assets on relative fair value basis		$ 27
Business acquisition, purchase price allocation, property, plants and equipment		19
Business acquisition, purchase price allocation, intangible assets		$ 8