Cuticle
The thin outer layer of each hair, made of overlapping scales like roof tiles.
Also: hair cuticle
The cuticle is the outermost layer of a hair strand. It is made of flat, overlapping cells that point towards the tips, like tiles on a roof. When the cuticle lies flat, hair reflects light and looks glossy; when it is raised by chemicals, heat or rough handling, hair can look dull and tangle more. Brushing from roots to ends follows the direction of the scales, which is one reason hair is detangled from the ends upwards.