Silkworms produce the natural silk. There are two distinct kind of silk: Tussah silk and Mulberry Silk.
The Tussah silk is wild silkworm produced silk. It is less expensive and less quality silk. Human raised silkworms produce the Mulberry Silk. Mulberry Silk has better quality than Tussah. Depending on how to handle the silkworm cocoons, the silk can be divided into hand made and machine made. Also, depending on the silk quality, the silk can be divided into different class. The longer the fiber of silk, the better the quality.
The silk can be used to make sheet or comforter fill-in. Silk sheet can be washed but comforter is not recommended to wash.