A thin hard wearing layer of cells on the surface of the skin which is removed before tanning. Its main constituent is the protein keratin, which is also the main constituent of hair.

The outer part of the epidermis consists of dead skin cells while the inner layer consists of soft living cells which are easily disintegrated by alkalis. Both epidermis and hair are removed during the liming process.

The removal of the epidermis leaves a smooth surface which becomes the characteristic grain surface of the leather.