On September 21, 2009, Cabot Corporation (the "Company") entered into an underwriting agreement (the "Underwriting Agreement") with J.P. Morgan Securities, Inc. and Banc of America Securities LLC, as representatives of the several underwriters named in Schedule 1 thereto (collectively, the "Underwriters"), pursuant to which the Company agreed to sell, and the Underwriters agreed to purchase, upon the terms and subject to the conditions set forth therein, $300 million aggregate principal amount of 5.00% notes due 2016 (the "Notes").

On September 24, 2009, the Company completed the issuance and sale of the Notes. In connection with the issuance and sale of the Notes, the Company entered into a supplemental indenture (the "First Supplemental Indenture") with U.S. Bank National Association, as trustee, relating to the Notes.

The Notes were registered on Form S-3 under the Securities Act of 1933 (Registration Statement No. 333-162021) (the "Registration Statement"). In order to furnish certain exhibits for incorporation by reference into the Registration Statement, the Company is filing the Underwriting Agreement, the First Supplemental Indenture, the computation of ratio of pro forma earnings to fixed charge and the opinion of Ropes & Gray LLP relating to the validity of the Notes as exhibits to this filing.

(d) Exhibits.

1.1     Underwriting Agreement dated as of September 21, 2009 by and among Cabot
        Corporation and J.P. Morgan Securities, Inc. and Banc of America
        Securities LLC, as representatives of the several underwriters named in
        Schedule 1 thereto.

4.1     First Supplemental Indenture dated as of September 24, 2009 between Cabot
        Corporation, as issuer, and U.S. Bank National Association, as Trustee,
        including the form of Global Note attached as Annex A thereto,
        supplementing the Indenture dated as of September 21, 2009.

5.1     Opinion of Ropes & Gray LLP as to the validity of the Notes.

12.1    Computation of Ratio of Pro Forma Earnings to Fixed Charges.

23.1    Consent of Ropes & Gray LLP (included in Exhibit 5.1).