Carbonized wool has undergone an acid-based process to destroy embedded vegetable matter such as burrs and seeds, leaving a cleaner fiber. Degreased non-carbonized wool (510121/510129) has had lanolin removed but retains any vegetable contamination. The distinction matters both for classification and for downstream spinning mill requirements, since carbonized wool is typically used where a very clean fiber is needed.

The US tariff schedule separates shorn wool (510111, 510121) from pulled or otherwise non-shorn wool (510119, 510129) at the subheading level, and duty rates can differ between them. Importers should verify the applicable rate for each specific line, as tariff-rate-quota provisions may also apply depending on the subheading and country of origin.