Silk is a natural protein fiber, some forms of which can be woven into textiles. The best-known type of silk is obtained from cocoons made by the llarvae the mulberry silkworm, reared in captivity. The shimmering appearance for which silk is prized comes from the fibers' triangular prism-like structure which allows silk cloth to refract incoming light at different angles.

Silks are produced by several other insects, but only the silk of moth caterpillars has been used for textile manufacture. There has been some research into other silks, which differ at the molecular level. Silks are mainly produced by the larvae of insects that complete metamorphosis, but also by some adult insects such as webspinners. Silk production is especially common in the hymenoptera likes bees, wasps, and ants and is sometimes used in nest construction. Other types of arthropod produce silk, most notably various aracnids such as spiders or spider silk.

Spider silk, also known as gossamer, is a fiber spun by spiders. Spider silk is a remarkably strong material. Its tensile strength is comparable to that of high-grade steel. However, spider silk is much less dense than steel. It's tensile strength to density ratio is roughly five times higher than that of steel. In fact, a strand of spider silk long enough to circle the earth.