Felt is manufactured by pressing and matting animal hair. Bristles, the short, stiff hair of hogs, are used in making various kinds of brushes. The root and shaft. The part of a hair below the surface of the skin rests in a baglike structure called the follicle. The root, which is the lowest section of a hair, enlarges at the end into a soft, light-colored structure called the hair bulb.
Hair develops from the cells of the bulb, which divide rapidly.
A structure called the papilla projects into the hair bulb at the base of the follicle. It contains connective tissue and blood vessels that supply the blood necessary for the growing cells. The cells of the hair bulb move upward as new cells begin to form beneath them. As these cells move higher, they are cut off from their supply of nourishment and start to form a hard protein called keratin. The formation of keratin is called keratinization, and the hair cells die as it occurs.