U.S. exports of Isobutene-Isoprene (Butyl) Rubber (IIR) (HS 400231) totaled $4.1M in August 2026.
Importers of Isobutene-Isoprene (Butyl) Rubber (IIR) paid $24K in duties in August 2026, an average duty rate of 2.47% — duty actually collected as a share of the imports that cleared customs, not the published tariff schedule. Isobutene-Isoprene (Butyl) Rubber (IIR) imports of $954K in August 2026 ran 26% below the year-to-date monthly average of $1.3M.
Last updated: August 2026 dataButyl rubber's near-impermeable barrier to gases makes it the material of choice for tire inner tubes and liners, pharmaceutical stoppers, and industrial seals where air or moisture retention is critical. Canada dominates US supply — a reflection of the major IIR production facilities operated in Canada by global elastomer producers — with India and Thailand also contributing. The entire heading is covered by tariff line 4002310000. Mooney viscosity and isoprene content are the primary specification parameters that differentiate IIR grades for tire versus pharmaceutical applications.
AI-written summary of the official U.S. Census Bureau trade figures on this page — verify before relying on it.
36 import shipments a month
IIR's extremely low gas permeability and chemical inertness make it suitable for vial stoppers and syringe plungers where container integrity is paramount. When butyl rubber is imported as a finished pharmaceutical closure rather than as raw polymer, it may be subject to FDA review as a drug-contact material. Raw IIR polymer classified under 4002310000 does not itself trigger FDA admissibility review, but downstream finished closures would. Importers should confirm the form of the goods and consult a customs broker if the material is partially fabricated.
Canada's proximity and USMCA trade relationship provide US buyers with logistical and cost advantages, but the concentration of IIR production in a small number of North American facilities means supply disruptions — whether from plant outages or feedstock shortages — can have outsized market impact. Buyers with critical IIR requirements often maintain safety stock or qualify secondary suppliers from India or Japan to hedge against single-source exposure.
Subheading 9 of 14 in heading 4002
Subheading 400231 · $4.1M of $240.3M
ImportsExports
Imports
$954KYoY · free account
Exports
$4.1MYoY · free account
12-mo low · imports
Low · free accountOver the twelve months to August 2026, the U.S. imported $14.4M of Isobutene-Isoprene (Butyl) Rubber (IIR) and exported $50.7M.
Through August 2026. Source: U.S. Census Bureau.
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HS10 import codes under this HS6 parent, each with its own page. Source: U.S. Harmonized Tariff Schedule.
| Code | Description | Imports for consumption | Average duty rate | Dutiable Share | Duty Collected |
|---|---|---|---|---|---|
| 4002310000 | Isobutene-Isoprene (Butyl) Rubber (Iir) | $954K | 2.47% | 42.32% | $24K |
HS10 export codes under this HS6 parent, each with its own page. Source: U.S. Schedule B export classification.
| Code | Description | Export Value |
|---|---|---|
| 4002310000 | Isobutene-Isoprene (Butyl) Rubber (Iir) | $4.1M |
Import lines come from the U.S. Harmonized Tariff Schedule and export lines from Schedule B. The two are numbered by different agencies, so the same 10-digit code can appear in both tables describing a different product.
Exports · August 2026
destination
Belgium and Mexico together take 66% of it.
customs district
origin
entry
rate provision · imports
57.7% enters free of duty; duty collected equals 2.47% of imports for consumption.