The Treasury Department and IRS have published several Notices of Determination adding substances to the list of taxable substances subject to Superfund excise taxes (Notice of Determination (May 31, 2024), Notice of Determination (August 4, 2025), Notice of Determination (September 17, 2025)).

Other than Polyoxymethylene, which became taxable in the fourth quarter of 2024, all the newly listed taxable substances become taxable upon import and sale on or after January 1, 2026.

Superfund taxes paid on substances that are listed in the Notices of Determination and ultimately exported are eligible for refund. The Notice of Determination listing each substance specifies how far back a taxpayer can go to claim a refund, with many eligible claims dating back to July 1, 2022. While there are basic forms for filing refund claims, the IRS is still developing procedures and documentation requirements for examining the refund claims for exported taxable substances.

The attached table lists the 61 newly-added taxable substances, along with the conversion factor(s), tax rate, Harmonized Tariff Schedule of the United States (HTSUS) number, and the tax effective date for each substance. Importers subject to the excise tax under IRC Section 4671(a) for selling or using these taxable substances should use this information when calculating and reporting their Superfund excise tax liability on substances imported into the United States (see Tax Alert 2022-0018).

Implications

Taxpayers should evaluate their transactions found in the U.S. Customs Automated Commercial Environment (ACE) to determine whether they have imported or exported any of the newly-listed taxable substances. As no tax is due on imports of the newly-listed taxable substances before January 1, 2026 (other than Polyoxymethylene), taxpayers should consider making deposits on sales of newly listed imported taxable substances that are made after this date.

Where applicable, taxpayers should consider the availability of refund claims on the export of the newly-listed taxable substances for tax periods beginning on or after July 1, 2022. For Superfund taxes paid in the third quarter of 2022, taxpayers have until October 31, 2025, to file a refund claim. Refund claims can still be filed even though the IRS is in the process of updating their procedures.