6109.90.15.10 - Underwear (459)

This HTS category, 6109.90.15.10, specifically classifies men's or boys' underwear, knitted or crocheted, originating from textile materials other than cotton or man-made fibers, and made of wool with long sleeves. This includes items like long-sleeved thermal underwear tops, base layers, and undershirts designed for warmth, falling under the broader umbrella of "underwear" as defined within HTS Chapter 61.

Distinguishing this category from its sibling, 6109.90.15.20 (Other), is crucial. While both fall under "Of wool, with long sleeves" and "Men's or boys'", this specific subcategory is exclusively for items classified as "Underwear." The sibling category likely encompasses other types of knitted or crocheted garments of wool with long sleeves for men or boys that are not considered underwear, such as certain types of casual shirts or loungewear tops.

As this is a leaf node, there are no further subcategories to introduce. Classification under 6109.90.15.10 therefore hinges on the garment being knitted or crocheted, made of wool, possessing long sleeves, intended for men or boys, and functioning as underwear. The primary determinant is the garment's intended use as an underlayer, in contrast to outerwear or other types of apparel.