Common blends include cotton/polyester, cotton/viscose, and cotton/linen. For classification purposes, the key question is whether cotton remains the predominant fiber by weight or whether another fiber exceeds cotton's share — if a non-cotton fiber becomes the majority component, the yarn may shift to a different SITC or HTS heading altogether. Importers should obtain mill certificates specifying each fiber's weight percentage to ensure the correct heading is applied.

Yes — CBP has authority to request laboratory fiber analysis if the declared fiber composition is questioned. If testing reveals that the cotton content differs materially from the declaration — particularly if it crosses the 85% threshold or changes the predominant fiber — CBP may reclassify the entry and assess additional duties or penalties. Maintaining supplier-issued fiber test reports and retaining them for five years after entry is a best practice for managing this risk.