EXHIBIT 23(i)

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We consent to the incorporation by reference in Registration Statement No. 333-64787 on Form S-3 and Nos. 333-03683, 333-19103, 333-19099, 333-82353, 333-96879, 333-96881, 333-136484, 333-134134 and 333-134133 on Form S-8 of our reports dated November 29, 2007 relating to the financial statements of Cabot Corporation (which report expresses an unqualified opinion and includes an explanatory paragraph relating to the adoption of Statement of Financial Accounting Standards No. 158, “Employers’ Accounting for Defined Benefit Pension and Other Postretirement Plans, an amendment of FASB Statements No. 86,88,106 and 132(R)”), and the effectiveness of Cabot Corporation’s internal control over financial reporting, appearing in this Annual Report on Form 10-K of Cabot Corporation for the year ended September 30, 2007.

/s/ Deloitte & Touche LLP

Boston, Massachusetts

November 29, 2007