Silk is not a hair, like other animal fibers, but it is a protein thread spun by silk worms. The thread is used to create the worm's cocoon. Each strand of thread can be over 1000 yards long! To make yarn, the strands are unwound from the cocoons, cut into staples and spun into silk yarn. Silk worms may be wild or cultivated; the wild ones produce a coarser fiber than the cultivated varieties.
The finest silks are produced from worms who are fed a diet of mulberry leaves. Because of the high level of care required to farm silk worms and producing yarn, pure silk yarn tends to be expensive. But silk blend yarns are affordable; and combining with wool, cotton, rayon and alpaca with silk produces truly beautiful yarns.