Heading 3201 is limited to tanning extracts and tannins of vegetable origin and their direct chemical derivatives. Synthetic organic tanning substances — regardless of whether they perform the same tanning function — are classified in heading 3202. The key criterion is whether the tanning substance originates from a plant source or is produced by organic synthesis.

Tannins and their salts, ethers, esters, and other derivatives remain in heading 3201 as long as they are derived from vegetable tanning extracts. However, if a derivative is more specifically described by a heading in another chapter — for example, as a defined chemical compound — the more specific heading takes precedence under GRI 3. A binding ruling is advisable for highly processed or chemically modified tannin derivatives.