The Cortex, the inner middle layer, is the most important and complex part of the hair.

Because it contains protein chains, hydrogen bonds, salt bonds and disulfide bonds, it is relevant for chemical services like coloring, perming, straightening or keratin treatments. Because of its inner structure, the Cortex is responsible for strength and flexibility. It also contains the pigments (melanin) that determine natural hair color.

A cortex cell contains Macrofibrils.

Each Macrofibril consists of Microfibrils.

Microfibril (Intermediar Filaments) consists of Protofibrils, each made of Protofilaments.

Each Protofilament is made of Alpha-Helices.

In the innermost the hair is made of disulfide, ionic and hydrogen bonds, that forms the Alpha-Helix.