Hair

A hair is essentially a very tall thin stack of flattish cells. The strength and toughness of hair comes from a protein coating on the surface. This protein has long tough filaments that tie the column of cells together along it's length. This is the same protein (keratin) that makes skin and fingernails tough.

The individual strands of hair can be round in cross section or more of a flattened oval, with flatter sections resulting in curlier hair. Think of string vs ribbon. 

Each hair goes through a phase of growth, followed by a period of near static length, before being shed and growing anew. Your maximum hair length is determined by the duration and rate of the growth period. Typical values would be a duration of five years at six inches a year, resulting in hair two and a half feet long. But depending on the individual it could be twice as long, mostly depending on a longer growth duration. World record hair lengths can be over 18 feet long, but it's unclear how much such lengths rely on braiding or matting. 

If you have a tabby cat, look closely at it's hairs. You may observe that in addition to body stripes, the individual hairs may, themselves, be striped. These are called agouti hairs and result in a finely speckled pattern.