Peptones are defined by their solubility and the degree of protein hydrolysis — they are water-soluble and not coagulated by heat. Products hydrolyzed further into free amino acids typically fall outside this heading, while those retaining peptide character remain here. A binding ruling from CBP is advisable when the hydrolysis profile is ambiguous.

Hide powder — finely ground, defatted animal hide — is used as a reference substrate in leather-tanning research and enzyme-activity testing. It may be chromed or unchromed; both forms are classified here, making this heading unusual in spanning both biochemical reagents and a leather-industry input.