Silk fibers come from the spun cocoon of the Mulberry silkworm moth, or Bombyx mori. Each silkworm pupae forms a single filament about 0.62 miles in length. Cocoons are treated with steam or boiling water, and each cocoon is carefully unwound. Anywhere between four and eight cocoons are processed simultaneously to create a single strand of silk thread.
Raw silk contains sericin, a substance washed out before the fibers are made into fabric. It takes about 2,500 silkworms to make 1 pound of raw silk. Four types of silk threads are produced from the raw fibers, such as crepe, tram, thrown singles, and organzine. Crepe silk is produced by twisting two or more threads of silk together in multiple directions. Tram is made by twisting threads of silk in just one way. Thrown singles include just one silk thread twisted in a single direction, and organzine is made of two or three threads twisted in one direction before twisting in the opposite direction.
Leftover silk is spun into yarn and sold as spun silk. These fibers have lower quality than reeled silk, and spun silk yarn is much cheaper. Combed silk is also sold as a leftover of the reeling process.
Mulberry silkworm moths lay between 300 and 400 eggs and die within two weeks. The eggs grow into larva that eat mulberry leaves. The larva then pupate and spin the silky cocoons that go into silk fibers. Silk production originated in ancient China.