4106.31 - In the wet state (including wet-blue):

This HTS classification covers tanned or crust skins of swine that are in a wet state, specifically those that have undergone a tanning process but remain moist. These are often referred to as "wet-blue" due to the chromium salts used in the tanning process which impart a bluish hue to the skins. The skins are characterized by the absence of wool or hair and can be split but not further prepared beyond the tanning stage.

This category is distinguished from its sibling, 4106.32.00.00, which covers swine skins in the dry state or "crust." While both originate from swine and are tanned, the key differentiator here is the moisture content; 4106.31 pertains to skins still in a wet or semi-wet condition post-tanning, whereas 4106.32 deals with skins that have been dried to a crust state.

Within this category, two subcategories exist to further refine the classification. 4106.31.10.00 specifically addresses "wet blues," which are skins tanned with chromium salts, aligning with the common understanding of this tanning method. The remaining wet-state swine skins, not fitting the specific description of "wet blues," are classified under 4106.31.90.00 as "Other." This allows for the accurate categorization of various wet-state tanned swine skins based on their specific processing characteristics.