Importers of HS 3903.90 (methyl methacrylate-butadiene-styrene (mbs) copolymers) from Mexico actually paid 16.5% on the taxed portion of the value in 2026-06 — 0.07% across everything shipped, taxed or not. Measured from official duty receipts, not the rulebook: the statutory MFN base rate on this code is 6.5%. Over the window the rate on the taxed portion moved 6.5% → 16.5%, with the largest single step -31.5pp in 2026-03. Measured from official US duty receipts · as-of 2026-06 · confidence: measured, not modelled. The HTS base rate is 6.5% — importers actually paid 16.5%, so the trade-war overlay added 10 pts, measured at the border (not a summed rulebook estimate). Reproduce exactly: tariff_story(hs: "3903.90", origin: "Mexico") · see it at trimtabist.com/tariffs
HS 3903.90. The schedule base rate is 6.5%; importers from Mexico actually paid 16.5% on the dutiable value in 2026-06 — the trade-war overlay added 10 points, measured at the border. Measured, not modelled.
Over the window the collected rate moved 6.5% (2023-07) → 16.5% (2026-06), largest single step -31.5pp in 2026-03.
Mexico's lower duty (0.07% vs 33.9%) lets it price up to 33.8% above China at the factory and still match on duty-inclusive customs cost. But on the LATEST measured prices, Mexico actually lands cheaper — $1.92/kg vs $7.81/kg (duty in, freight out).
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 · reproduce: tariff_story(hs: "3903.90", origin: "Mexico") via /connect. Not customs or legal advice.