6406.10.90.40 - Of man-made fibers (669)

This HTS subcategory, 6406.10.90.40, specifically covers parts of footwear, particularly uppers and their components, that are exclusively constructed from man-made fibers. This includes synthetic and regenerated fibers, excluding natural fibers like cotton, wool, or fine animal hair. Examples within this classification would be the fabric sections forming the upper portion of athletic shoes, casual footwear, or boots made entirely from materials such as polyester, nylon, or rayon.

The key differentiator for this category lies in its material composition. It is distinct from its sibling category 6406.10.90.20, which is reserved for uppers and parts thereof made from wool or fine animal hair. Furthermore, it differs from the broader sibling category 6406.10.90.60, which encompasses any remaining "other" materials not specifically defined by the preceding classifications within this level.

As this is a leaf node in the HTS classification system, there are no further subcategories. Therefore, the classification decision rests solely on confirming that the footwear part in question is indeed an upper or component thereof, and that its constituent material is exclusively man-made fibers.