Human hair is said to be made of 100% human hair, however I have seen strands of thick string in it. Now real human hair is made up of keratin which is a protein. Hair that has great cuticles will be stronger without split ends, when the cuticle becomes damaged then the hair will split and break off. Melanin gives hair its color. Now if you are talking about hair weave, then you need to know that as the old saying goes they do not get the hair from Chinese women who donate it, the weaves would be more expensive if that was the case.
Clue: keratin. What is human hair made of? blurts out the winner. Intriguingly all manner of human hair grows at the follicle and consists primarily of the protein keratin. You can find more information here: http://en.wikipedia.org/wiki/Keratin