The fibrous layer of the hair is also called the cortex (bark) or fibre stem. It is located under the cuticle layer. The cortex makes up about 80 % of the hair. The fibre layer consists of fibre bundles, which in turn consist of the finest keratin fibres, the so-called fibrils. The individual keratin fibres themselves consist of cortex cells that are held together with a cell membrane. The stronger and more elastic this connection is, the more tear-resistant the hair is.