High-performance racing suits with bonded or taped seams but a knit base fabric are generally still classified as knitted swimwear, since the seam treatment does not constitute a coating or lamination of the fabric itself. However, suits where the fabric is laminated with a polyurethane or rubber layer may be redirected to the coated-fabric garment heading. The fabric's technical specification sheet is the key document for making this determination.

CBP distinguishes swimwear from underwear based on design features, fiber content, and intended use. Swimwear typically uses chlorine-resistant synthetic fibers (nylon, polyester), features a lining or gusset suited for aquatic use, and is marketed and labeled as swimwear. Underwear briefs are generally cotton or cotton-blend and lack these features. Misclassifying underwear as swimwear (or vice versa) can result in duty underpayment; accurate product descriptions and fiber declarations on the commercial invoice are essential.