Fiber composition (natural vs. synthetic, and specific fiber type), whether the yarn is single or multiple (plied or cabled), the number of turns per meter (twist), and whether it is put up for retail sale are the primary classification determinants. These factors map to different HTS chapters and headings, making laboratory fiber analysis a common tool for customs brokers handling ambiguous shipments.

Section 301 tariffs on Chinese-origin goods have increased landed costs for polyester, nylon, and other synthetic yarns sourced from China, leading many importers to diversify toward suppliers in Vietnam, India, and other countries not subject to those measures. However, importers must verify that transshipment through third countries does not trigger country-of-origin fraud concerns, which CBP actively investigates in the textile sector.