The human hair shaft is made up of protein, called keratin, in three layers. The inner layer is called the medulla and may not be present. The next layer is the cortex and the outer layer is the cuticle. The cortex makes up the majority of the hair shaft. The cuticle is formed by tightly packed scales in an overlapping structure similar to roof shingles. Most hair-conditioning products attempt to affect the cuticle. There are pigment cells that are distributed throughout the cortex, giving the hair its characteristic color. The hair cuticle is the first line of defense against all forms of damage; it acts as a protective barrier for the softer inner structures, including the medulla and cortex.
The cuticle is responsible for much of the mechanical strength of the hair fiber. A healthy cuticle is more than just a protective layer, as the cuticle also controls the water content of the fiber. Much of the shine that makes healthy hair so attractive is due to the cuticle. In the hair industry, the only way to obtain the very best hair (with cuticle intact and facing the same direction)
*Hair extensions made of true virgin, raw (cuticle hair) have the most durability and ease of use as the integrity of the hair has not been broken or altered by the method of collection. This continues to be true if this hair is then simply wefted or sewn on a track, without any processed chemical or steamed done on the hair.