Silk is the only natural fiber from animals that is continuously produced and obtained from the cocoons of the larvae of the mulberry silkworm (Bombyx mori).
Silk is a very ancient and valuable material. It is very light, elegant and soft. Usually silk is cultivated, but there is also wild-silk, called Tussah, that is named after the cocoons of the Tussah moths.
You can find more information about Silk (SE) in Wikipedia.