(b) On February 25, 2026, Paul T. Stecko informed the Board of Directors (the "Board") of Packaging Corporation of America ("PCA") that he has decided to retire from service on the Board and will not stand for reelection to the Board at the 2026 Annual Meeting of Stockholders (the "Annual Meeting"). Mr. Stecko's decision to retire from the Board is not the result of any disagreement with PCA on any matter relating to its operations, policies, practices or otherwise, and he will continue to serve as a director of PCA until the expiration of his term at the Annual Meeting. Effective at the Annual Meeting, the size of PCA's Board will be reduced from ten to nine directors.

(c)Fabian C. Strauss, age 45, PCA's Vice President, Controller and Treasurer, was promoted to PCA's Senior Vice President - Finance, Controller & Treasurer on March 1, 2026, and he will serve as PCA's principal accounting officer. Mr. Strauss joined PCA in January 2022 as Executive Director, Assistant Controller, and he was promoted to his current position in 2024. Immediately prior to joining PCA, Mr. Strauss was the Chief Accounting Officer at EOS Energy Storage, Inc. from November 2020 until January 2022. Mr. Strauss also previously worked for PriceWaterhouseCooopers LLP, Walgreens Company, and Treehouse Foods. Mr. Strauss will receive an annual base salary of $455,000, and he is eligible for an annual incentive award under PCA's Executive Incentive Compensation Plan, as awarded by the Compensation Committee (the "Committee") of the Board, and awards under PCA's Second Amended and Restated 1999 Long-Term Equity Incentive Plan (the "Long-Term Equity Incentive Plan"), as awarded by the Compensation Subcommittee (the "Subcommittee") of the Committee.

There are no family relationships between Mr. Strauss and any director or executive officer of PCA. No agreements were entered into with Mr. Strauss in connection with his appointment to the new position. Mr. Strauss is not party to any transaction that requires disclosure under Item 404(a) of Regulation S-K.

(e)On February 25, 2026, the Subcommittee approved new forms of equity award agreements for long-termincentive ("LTI") grants of performance units based on total shareholder return ("TSR performance units") and performance units based on return on invested capital ("ROIC performance units"), as well as a new form of grants of restricted stock units ("RSUs"), all under the Long-Term Equity Incentive Plan. These new forms will be used for awards made on and after February 25, 2026 and prior awards forms were not changed. The approved forms of equity award agreements are substantially similar to the prior year forms, with amendments that include the following:

"Retirement" is defined for purposes of the above agreements as termination on or after the date the participant attains at least age 55 and the sum of the participant's age and service equals at least 70 (and the termination does not occur for any other reason).

The other material terms of the forms of equity award agreements remain substantially unchanged. The new forms of ROIC performance unit agreement and TSR performance unit agreement, as well as the form of RSU agreement, will be utilized beginning with grants of fiscal year 2026 LTI compensation.

The foregoing summary of the forms of award agreements is qualified in its entirety by reference to the full text of such agreements, copies of which are filed as Exhibits 10.1, 10.2, and 10.3 hereto, and incorporated herein by reference.

(e) PCA and Robert Mundy, PCA's former Executive Vice President and Chief Financial Officer, entered into an agreement, dated as of March 1, 2026, in connection with Mr. Mundy's retirement (which was previously disclosed pursuant to Item 5.02 of PCA's Current Report on Form 8-K, filed with the SEC on February 28, 2025). The agreement provides that Mr. Mundy retired as Special Advisor to PCA, effective March 1, 2026 (the "Retirement Date"). Pursuant to the agreement, Mr. Mundy will be subject to customary confidentiality, non-competition and non-solicitation covenants. Subject to Mr. Mundy's continued compliance with such covenants, all of Mr. Mundy's 9,928 outstanding shares of restricted stock vest as of the Retirement Date. In addition, Mr. Mundy will continue to vest in his 3,900 outstanding TSR performance units and his 9,928 outstanding ROIC performance units, and all such performance units will vest on the originally scheduled dates provided for in the award agreements in accordance with the terms of such awards. The foregoing summary is qualified in its entirety by reference to the entire agreement, a copy of which is filed as Exhibit 10.4 hereto, and incorporated herein by reference.