Two rubbers join the Superfund excise tax list on October 1

Notice 2026-43 was carried in Internal Revenue Bulletin 2026-29 on July 13, following publication in the Federal Register on June 26. It adds two substances to the section 4672 list of taxable substances. Chloro-isobutene-isoprene rubber carries a rate of $9.46 a ton. Ethylene-propylene-dicyclopentadiene rubber carries $9.64. The section 4671 tax on importers takes effect October 1, 2026, while the effective date for refund claims under section 4662(e) reaches back to April 1, 2023. The first substance is a halogenated copolymer of butylene and isoprene, used in tire inner tubes, hoses, seals, membranes, tank linings, conveyor belts and protective clothing. The taxable chemicals butylene, chlorine and sodium hydroxide make up 97.36% of its inputs by weight under the predominant production method.