Exhibit 3.1

AMENDMENT TO THE BY-LAWS OF CABOT CORPORATION

The By-laws of Cabot Corporation were amended, effective January 8, 2016, to add the following new Section 16:

Section 16. Exclusive Forum.

16.1 Unless the Corporation consents in writing to the selection of an alternative forum, the sole and exclusive forum for (i) any derivative action or proceeding brought on behalf of the Corporation, (ii) any action asserting a claim of breach of a fiduciary duty owed by any director or officer or other employee of the Corporation to the Corporation or the Corporation’s stockholders, (iii) any action asserting a claim against the Corporation or any director or officer or other employee of the Corporation arising pursuant to any provision of the Delaware General Corporation Law or the Corporation’s Certificate of Incorporation or Bylaws (as either may be amended from time to time), or (iv) any action asserting a claim against the Corporation or any director or officer or other employee of the Corporation governed by the internal affairs doctrine shall be a state court located within the State of Delaware (or, if no state court located within the State of Delaware has jurisdiction, the federal district court for the District of Delaware), in all cases subject to the court’s having personal jurisdiction over the indispensable parties named as defendants. Any person or entity purchasing or otherwise acquiring any interest in the shares of capital stock of the Corporation will be deemed to have notice of and consented to the provisions of this Section 16.

16.2 If any Foreign Action (as defined below) is filed in the name of any stockholder, such stockholder will be deemed to have consented to (i) the personal jurisdiction of the state and federal courts located within the State of Delaware in connection with any action brought in any such court to enforce Section 16.1 above (an “FSC Enforcement Action”) and (ii) having service of process made upon such stockholder in any such FSC Enforcement Action by service upon such stockholder’s counsel in the Foreign Action as agent for such stockholder. A “Foreign Action” means any action the subject matter of which is within the scope of Section 16.1 that is filed in a court other than a court located within the State of Delaware.