7410.21 - Of refined copper:

This HTS category, 7410.21, specifically classifies copper foil that is of refined copper and has a thickness not exceeding 0.15 mm, excluding any backing material. It encompasses such foil that is backed with materials like paper, paperboard, plastics, or similar substances. The key defining features are the material being refined copper, its thinness, and the presence of a backing layer.

This category is distinguished from its sibling, 7410.22, which covers copper foil of copper alloys. While both concern thin copper foil with backing, the distinction lies in the base metal composition; 7410.21 strictly applies to pure, refined copper, whereas 7410.22 pertains to foils made from copper mixed with other metals.

Within this category, further subdivisions exist to address specific product types. The subcategory 7410.21.30 covers copper clad laminates, which are composite materials often used in electronics manufacturing. The remaining products that fit the broader description of refined copper foil with backing, but are not copper clad laminates, fall under the "Other" subcategory, 7410.21.60.00.