Clearwater Paper Corp

As of June 30, 2025, our Chief Executive Officer (CEO) and Chief Financial Officer (CFO) have carried out, with the participation of our Disclosure Committee and management, an evaluation of the effectiveness of our disclosure controls and procedures, as defined in Rule 13a-15(e) under the Securities Exchange Act of 1934 (the Act). Based upon this evaluation, the CEO and CFO have concluded that our disclosure controls and procedures are effective to provide reasonable assurance that material information required to be disclosed by us in reports we file under the Act is recorded, processed, summarized and reported within the time periods specified in the Securities and Exchange Commission rules and forms and that information required to be disclosed by us in the reports we file or submit under the Act is accumulated and communicated to our management, including our CEO and CFO, as appropriate to allow timely decisions regarding required disclosure.

Changes in Internal Control Over Financial Reporting

We evaluated changes in our internal control over financial reporting that occurred during the quarter ended June 30, 2025.

The financial controls for Augusta Pulp and Paperboard operations (acquired in May 2024) were eligible for a one-year

exemption from the requirements of Section 404 and had been excluded through April 30, 2025. As of May 1, 2025, we updated our internal controls over financial reporting, as necessary, to support the integration of this mill. Except as it relates to the integration of the Augusta Acquisition, there have been no changes in our internal control over financial reporting during the quarter ended June 30, 2025 that has materially affected, or is likely to materially affect, our internal control over financial reporting.

Part II