Heading 380993 covers finishing agents, dye carriers, and preparations whose primary function is to modify the surface appearance, color, or structural properties of leather during tanning and finishing. Heading 3403 covers lubricating preparations for leather, such as fat-liquors whose primary function is to lubricate and soften the fiber structure. When a product performs both functions, classification follows the primary commercial purpose; a product marketed and used principally as a fat-liquor belongs in 3403, while one marketed as a finishing or dyeing auxiliary belongs in 380993.

In practice, most suppliers can provide a certificate of analysis or formulation disclosure that states the aromatic-substance content by weight. When that documentation is unavailable or the content is near the 5% threshold, CBP may request laboratory analysis to confirm classification. Importers should proactively obtain formulation data from their supplier and retain it as part of the entry record, as it is the most straightforward way to defend the chosen 10-digit line in a CBP audit.