Yarn containing 85% or more cotton by weight falls under 520710, while yarn with less than 85% cotton — typically blended with wool, acrylic, or other fibers — falls under 520790. The fiber content must be determined by weight of the total fiber composition, and the blend percentage should be confirmed by laboratory testing if there is any doubt.

The defining criterion is the retail presentation: yarn under 5207 must be put up for retail sale — on cards, balls, tubes, or similar small packages intended for the final consumer. Yarn on large industrial cones or in bulk form for textile mills is classified under 5205 (combed or carded single yarn) or 5206 (multiple or cabled yarn), regardless of fiber content.