The 85% threshold is measured by weight of synthetic staple fibers relative to the total fabric weight. A fabric that falls below 85% synthetic staple fiber content shifts to headings 5513 or 5514 if the secondary fiber is mainly cotton, or to 5515 if mixed mainly with other materials. Accurate fiber content testing is essential to avoid misclassification.

Finishing state determines the specific subheading — for example, unbleached or bleached polyester fabrics fall under 551211, while printed, dyed, or yarn-dyed versions fall under 551219 — and different subheadings can carry different duty rates. Importers should confirm the finishing state of the fabric before entry to ensure the correct tariff line is declared.