Yarn classified here is produced from continuous filaments reeled directly from silkworm cocoons, giving it a smooth, lustrous character. Spun silk yarn, by contrast, is made from shorter fibers recovered from broken cocoons, pierced cocoons, or other silk waste, and falls under a separate heading. The production method — not the fiber origin — determines which heading applies.

Silk yarn imported for further manufacturing is subject to standard textile import requirements including country-of-origin marking. If the yarn will be incorporated into consumer textile products sold in the US, downstream labeling must comply with the Textile Fiber Products Identification Act, which requires accurate fiber content disclosure. Classification is complex; consult a licensed customs broker for specific entry guidance.