SecProbe.io

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
WASHINGTON, D.C. 20549-4631

       DIVISION OF
CORPORATION FINANCE

Mail Stop 4631
January 25, 2010
 Mr. Eduardo E. Cordeiro Executive Vice President and Chief Financial Officer Cabot Corporation Two Seaport Lane, Suite 1300 Boston, MA  02210
 RE: Form 10-K for the year ended September 30, 2009
  File No. 1-5667

Dear Mr. Cordeiro:
We have reviewed your filing and have the following comments.  If you disagree
with a comment, we will consider your explanation as to why our comment is inapplicable or a revision is unnecessary.  Pl ease be as detailed as necessary in your
explanation.  In some of our comments, we may ask you to provide us with information so we may better understand your disclosure.  After reviewing this information, we may
or may not raise additional comments.   Please understand that the purpose of our re view process is to assist you in your
compliance with the applicable disclosure  requirements and to  enhance the overall
disclosure in your filing.  We look forward to  working with you in these respects.  We
welcome any questions you may have about our comments or on any other aspect of our review.  Feel free to call us at the telephone numbers listed at the end of this letter.

FORM 10-K FOR THE YEAR ENDED SEPTEMBER 30, 2009

 Item 1 - Business, page 3

 Research and Development, page 11

1. In future filings please include a cross-re ference here to your discussion on page
39 regarding your Research and Technical Expenses.

Mr. Eduardo E. Cordeiro
Cabot Corporation
January 25, 2010 Page 2 of 6   Legal Proceedings, page 21

 Environmental Proceedings, page 21

2. We note your April 11, 2008 response to co mment three of our letter dated March
28, 2008.  We further note that at the end of  the fourth paragraph you continue to
disclose that the claims relative to Cabot are without merit without explaining the basis of such belief.  Please advise or ot herwise, in future filings comply with our
prior comment three in full.

3. In future filings please ensure your disclosure in this section complies with Item 103 of Regulation S-K, including disclosu re about the name of the court or
agency in which a proceeding is pending, the date instituted, the parties thereto,  a
description of the f actual basis alleged to underlie the proceeding and the relief
sought.  Please refer in partic ular to instruction 2 of It em 103 of Regulation S-K.
 Respirator Liabilities, page 22

4. We note your proposed disclosu re in response to comment four of our letter dated
March 28, 2008.  We are unable to locate disclosure regarding your total cash
payments with respect to the Aearo-related liabilities, as indicated at the end of
your proposed disclosure.  Please advise, or ot herwise, in future filings ensure that
your revised disclosure is responsive to our prior comment.
 Item 7 – Management’s Discussion and Analysis of Financial Condition and Results of
Operations, page 29
 Critical Accounting Policies, page 29

 Goodwill and Other Intangible Assets and Valuation of Long-Lived Assets, page 31

5. In the interest of providing readers w ith a better insight into management’s
judgments in accounting for goodwill, please disclose the following in future filings:
• The reporting unit level at which you test goodwill for impairment and your
basis for that determination;
• How you weight each of the methods used to value goodwill, including the
basis for that weighting;
• How the methodologies used for valui ng goodwill in the current year have
changed since the prior year; and
• To the extent that any of your reporting units have estimated fair values that
are not substantially in excess of the carrying value and to the extent that
goodwill for these reporting units, in th e aggregate or individually, if

Mr. Eduardo E. Cordeiro
Cabot Corporation
January 25, 2010 Page 3 of 6
impaired, could materially impact your operating results, please provide the
following disclosures for each of these reporting units in future filings:
• Identify the reporting unit;
• The percentage by which fair value exceeds the carrying value as of the
most-recent step-one test;
• The amount of goodwill;
• A description of the assumptions that drive the estimated fair value;
• A discussion of the uncertainty associ ated with the key assumptions.  For
example, to the extent that you have included assumptions in your
discounted cash flow model that materi ally deviates from your historical
results, please include a disc ussion of these assumptions; and
• A discussion of any potential events and/or circumstances that could have
a negative effect to the estimated fair value.
If you have determined that the estimated fair value substantially exceeds the carrying value for all of your reporting units, please disc lose this determination.
Please also provide the above disclosures, as ap plicable, for any long-lived assets
or asset groups for which you have dete rmined that undiscounted cash flows is
not substantially in excess of the carrying value and to the extent that the asset
amounts, in the aggregate or individua lly, could materially impact your operating
results or total shareholder’s equity.  Please refer to Item 303 of Regulation S-K and Sections 216 and 501.14 of the SEC’s Codification of Financial Reporting
Policies for guidance.  Please show us in your supplemental response what the revisions will look like.
 Cash Flows and Liquidity, page 46

6. We note your credit facility agreem ent, which expires on August 3, 2010,
contains various affirmative, negative and financial covenants, among other restrictions.  We further note that you in tend to replace the cred it facility when it
expires.  In future filings, please ensure  that you clearly disclose the specific
terms of any material debt covenants and whether you were in compliance with
the covenants as of the reporting date.  In addition, if it is reasonably likely that
you will not be in compliance with any of  your material debt covenants, please
disclose the required ratios/amounts as well as the actual ra tios/amounts as of
each reporting date.  This will allow readers to understand how much cushion there is between the requir ed ratios/amounts and the ac tual ratios/amounts.  Please
also consider showing the specific computations used to arrive at the actual
ratios/amounts with corresponding reconc iliations to US GAAP amounts, if
necessary.  See Sections I.D and IV.C of the SEC Interpretive Release No. 33-
8350.  Please show us in your supplemental response what the revisions will look like.

Mr. Eduardo E. Cordeiro
Cabot Corporation
January 25, 2010 Page 4 of 6   Item 8 – Financial Statements and Supplementary Data, page 53

 Note S – Income Taxes, page 92

7. Given your disclosure on page 92 th at you have recognized losses from
continuing operations in the U.S. for each  of the three years ended September 30,
2009, please enhance your disclosure in future  filings to discuss the nature of the
U.S. deferred tax assets which have not been offset by a valuation allowance and
how you determined that these would be re alized.  In this re gard, please address
the following:
• Please expand your discussion of the na ture of the positive and negative
evidence that you considered, how that evidence was weighted, and how that
evidence led you to determine it was not appropriate to r ecord a valuation
allowance on the remaining deferred income tax assets.  You should consider
discussing the significant estimates and assumptions used in your analysis.
Please discuss how you determined the amount of the valuation allowance to record;
• Please disclose the amount of pre-tax in come that you need to generate to
realize the deferred tax assets;
• Please include an explanation of the antic ipated future trends included in your
projections of future taxable income; and
• Please disclose that the deferred tax liabilities you are relying on in your
assessment of the realizability of your de ferred tax assets will reverse in the
same period and jurisdiction and are of the same character as the temporary
differences giving rise to th e deferred tax assets.
Please show us in your supplemental response what the revisions will look like.
 Note T – Commitments and Contingencies, page 96

 Contingencies, page 97

 Environmental Matters, page 97

8. Regarding the environmental matters wh ich you are a party t o, please confirm
there is not a reasonable possibility  that a loss exceeding amounts already
recognized may have been incurred and the amount of that additional loss is material.  If there is a reasonable possibil ity, please disclose in future filings the
estimated additional loss, or range of loss, or state that such an estimate cannot be
made as required by FASB ASC 450-20-50.  Refer to SAB Topic 5:Y as well.
Please show us in your supplemental response what the revisions will look like.

Mr. Eduardo E. Cordeiro
Cabot Corporation
January 25, 2010 Page 5 of 6   Respirator Liabilities, page 98

9. Please disclose the number of claims in connection with respiratory products at
each balance sheet date, the number of cl aims filed for each period presented, the
number of claims dismissed, settled, or otherwise resolved for each period, and
the average settlement amount and total costs per claim.  Also, please address
historical and expected tre nds in these amounts and thei r reasonably likely effects
on operating results and liquidity.  Re fer to Question 3 of SAB Topic 5:Y.
 Item 15.  Exhibits, Financial Statement Schedules

 10. We note that you have not filed the e xhibits and schedules to the Credit
Agreement dated August 3, 2005 (Exhibit 10(a)(i )).  Please advise.  Refer to Item
601(b)(10) of Regulation S-K.  Otherwise,  please file a complete copy of this
agreement with your next Exchange Act report.

*    *    *    *
 Please respond to these comments within  10 business days, or tell us when you
will provide us with a response.  Please provi de us with a response letter that keys your
responses to our comments and provides a ny requested information.  Detailed letters
greatly facilitate our review.  Please file your supplemental response on EDGAR as a correspondence file.  Please understand that we may have additional comments after reviewing your responses to our comments.
We urge all persons who are responsible for the accuracy and adequacy of the
disclosure in the filings reviewed by the staff to be certain that they have provided all information required under the Securities Ex change Act of 1934 and that they have
provided all information investors require fo r an informed decision.  Since the company
and its management are in possession of all f acts relating to a company’s disclosure, they
are responsible for the accuracy and adequacy  of the disclosures they have made.

In connection with responding to our comments, please provide, in writing, a
statement from the company acknowledging that:
• the company is responsible for the adequacy and accuracy of the disclosure in their filings;
• staff comments or changes to disclosure  in response to staff comments do not
foreclose the Commission from taking any action with respect to the filing; and
• the company may not assert staff comme nts as a defense in any proceeding
initiated by the Commission or any pers on under the federal s ecurities laws of
the United States.

Mr. Eduardo E. Cordeiro
Cabot Corporation January 25, 2010 Page 6 of 6     In addition, please be advi sed that the Division of En forcement has access to all
information you provide to the staff of the Divi sion of Corporation Fi nance in our review
of your filing or in response to our comments on your filing.
 You may contact Era Anagnosti, Staff A ttorney, at (202) 551-3369 or, in her
absence, Craig Slivka, Special Counsel, at (202) 551-3729 if you have any questions
regarding legal or disclosure matters.  Pleas e contact Jeffrey Gordon, Staff Accountant, at
(202) 551-3866 or, in his absence, Nudrat Sa lik, Staff Accountant, at (202) 551-3692 if
you have questions regarding comments on the fi nancial statements and related matters.

 Sincerely,
 Rufus Decker
 Accounting Branch Chief