Importers of HS 3923.21 (of polymers of ethylene) from Mexico actually paid 4.14% on the taxed portion of the value in 2026-06 — 0.25% across everything shipped, taxed or not. Measured from official duty receipts, not the rulebook: the statutory MFN base rate on this code is 3%. Over the window the rate on the taxed portion moved 3% → 4.14%, with the largest single step +11.5pp in 2025-03. Measured from official US duty receipts · as-of 2026-06 · confidence: measured, not modelled. The HTS base rate is 3% — importers actually paid 4.14%, so the trade-war overlay added 1.1 pts, measured at the border (not a summed rulebook estimate). Reproduce exactly: tariff_story(hs: "3923.21", origin: "Mexico") · see it at trimtabist.com/tariffs
HS 3923.21. The schedule base rate is 3%; importers from Mexico actually paid 4.14% on the dutiable value in 2026-06 — the trade-war overlay added 1.1 points, measured at the border. Measured, not modelled.
Over the window the collected rate moved 3% (2023-07) → 4.14% (2026-06), largest single step +11.5pp in 2025-03.
5 Chapter-99 measures name Mexico; scope mapping is partial (several annexes are PDFs) — absence never means exemption. They do not sum, and some are product-specific — the collected rate above is the composed truth.
All goods from Mexico · the whole tariff ledger · 2 CBP rulings cite this code · reproduce: tariff_story(hs: "3923.21", origin: "Mexico") via /connect. Not customs or legal advice.