The protein fibre of silk is composed mainly of fibroin and is produced by certain insect larvae to form cocoons. The best-known silk is obtained from the cocoons of the larvae of the mulberry silkworm Bombyx mori reared in captivity (sericulture). Silk is a natural fibre that is usually woven into textiles. The protein fibre of silk is composed from cocoons of the larvae of mulberry silkworms. Kapok fibre (also called silk cotton) and seeds from a Kapok tree on Flores island, Indonesia.