The Internal Revenue Service has moved to broaden the scope of taxable substances under the Superfund excise tax, adding two industrial rubber compounds to its official list.
The IRS published a notice of determinations on June 26, 2026, confirming that the taxable substances list is modified to include chloro-isobutene-isoprene rubber and ethylene-propylene-dicyclopentadiene rubber.
The determination was published in the Federal Register at 91 Fed. Reg. 38778, marking a formal expansion of the agency’s Superfund excise tax framework.
Arlanxeo USA LLC and Arlanxeo Canada Inc., importers and exporters of both chemicals, submitted the petitions requesting that the substances be added to the taxable list.
According to the petition for chloro-isobutene-isoprene rubber, the taxable chemicals butylene, chlorine, and sodium hydroxide constitute 97.36 percent by weight of the materials used to produce this substance.
That figure is based on the predominant method of production, a key criterion the IRS uses when evaluating petitions for inclusion on the taxable substances list.
For ethylene-propylene-dicyclopentadiene rubber, the IRS confirmed that the taxable chemicals ethylene and propylene constitute 98.80 percent by weight of the materials used to produce the substance.
Again, this assessment was made based on the predominant method of production used for the compound in question.
For purposes of the tax under Section 4671 of the Code, the additions to the list of taxable substances will be effective October 1, 2026.
However, for purposes of refund claims under Section 4662(e) of the Code, the additions were retroactively made effective from April 1, 2023.
The Superfund excise tax applies to a wide range of chemical substances and is designed to fund environmental cleanup efforts across the United States.
The inclusion of these two rubber compounds reflects the IRS’s ongoing effort to ensure that substances manufactured from already-taxable chemicals are captured within the excise tax framework.
Companies that have imported or exported either substance since April 2023 may wish to review their potential eligibility for refund claims under the applicable provisions of the Code.