4002.31.00.00 - Isobutene-isoprene (butyl) rubber (IIR)

This HTS category specifically covers isobutene-isoprene (butyl) rubber, commonly known as IIR. This synthetic rubber is characterized by its low gas permeability and excellent resistance to heat, ozone, and weathering. It is typically supplied in its primary forms, such as bales, or in plates, sheets, or strip. IIR is widely used in applications requiring airtightness, such as inner tubes for tires, seals, gaskets, and pharmaceutical stoppers.

The distinguishing factor for this category, 4002.31.00.00, lies in its precise identification of isobutene-isoprene (butyl) rubber. It differentiates itself from its sibling category, 4002.39.00.00, which encompasses "Other" synthetic rubbers and factice derived from oils, not otherwise specified in heading 4002. This means that while both fall under the broader classification of synthetic rubber, 4002.31.00.00 is exclusively for IIR.

As this is a leaf node within the HTS, there are no further subcategories to introduce. Classification within this heading relies on the specific identification of the material as isobutene-isoprene (butyl) rubber (IIR). Therefore, to correctly classify goods under 4002.31.00.00, importers and exporters must confirm that the product is indeed IIR and not another type of synthetic rubber.