Importers of HS 3920.10 (of polymers of ethylene) from Japan actually paid 13.7% on the taxed portion of the value in 2026-06 — 13.7% across everything shipped, taxed or not. Measured from official duty receipts, not the rulebook: the statutory MFN base rate on this code is 4.2%. Over the window the rate on the taxed portion moved 4.2% → 13.7%, with the largest single step +7.2pp in 2025-05. Measured from official US duty receipts · as-of 2026-06 · confidence: measured, not modelled. The HTS base rate is 4.2% — importers actually paid 13.7%, so the trade-war overlay added 9.5 pts, measured at the border (not a summed rulebook estimate). Reproduce exactly: tariff_story(hs: "3920.10", origin: "Japan") · see it at trimtabist.com/tariffs
HS 3920.10. The schedule base rate is 4.2%; importers from Japan actually paid 13.7% on the dutiable value in 2026-06 — the trade-war overlay added 9.5 points, measured at the border. Measured, not modelled.
Over the window the collected rate moved 4.2% (2023-07) → 13.7% (2026-06), largest single step +7.2pp in 2025-05.
Japan's lower duty (13.7% vs 39.05%) lets it price up to 22.3% above China at the factory and still match on duty-inclusive customs cost. But on the LATEST measured prices, China actually lands cheaper — $2.09/kg vs $4.48/kg (duty in, freight out).
12 Chapter-99 measures name Japan; 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 Japan · the whole tariff ledger · 3 CBP rulings cite this code · reproduce: tariff_story(hs: "3920.10", origin: "Japan") via /connect. Not customs or legal advice.