3907.99 - Other:

This HTS category, 3907.99, encompasses "Other" polyesters in their primary forms. It serves as a residual category for polyesters that do not fall under the more specific subheading for unsaturated polyesters (3907.91). These materials are typically synthetic polymers characterized by the presence of ester functional groups in their molecular backbone. Their applications are diverse, ranging from fibers and films to molded articles, often chosen for their mechanical properties, chemical resistance, and thermal stability.

The distinction from its sibling, 3907.91, is crucial. While 3907.91 specifically enumerates unsaturated polyesters, which often contain carbon-carbon double bonds that allow for cross-linking, this category 3907.99 includes all other polyesters that lack these unsaturated characteristics. This includes saturated polyesters like polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) in their primary resin forms, which are widely used in packaging, textiles, and engineering plastics.

Within this category, further subdivisions exist to refine the classification. Subheading 3907.99.20 specifically addresses thermoplastic liquid crystal aromatic polyester copolymers, a specialized group known for their exceptional strength and thermal properties. The remaining polyesters not meeting this specific criteria are classified under 3907.99.50, "Other," ensuring comprehensive coverage of the broad spectrum of polyester resins.