Thrown silk yarn under heading 5004 is produced by twisting or doubling continuous filaments reeled directly from cocoons—the fiber is never broken into short lengths. Spun silk yarn under heading 5005 is made by carding and spinning short-staple fibers derived from silk waste, noil, or broken filaments, analogous to how cotton or wool is spun. The continuity of the filament is the defining distinction.

Classification of mixed-fiber woven fabrics follows the essential character rule based on the chief weight of the constituent fibers. A fabric in which silk predominates by weight classifies under heading 5007. If another fiber—such as polyester or cotton—predominates by weight, the fabric moves to the chapter governing that fiber. The silk content percentage must be established to determine the correct chapter.