Animal fibre produced by certain insects as building material for cocoons and webs. In commercial use it refers almost entirely to filament from cocoons produced by the caterpillars of several moth species of the genus Bombyx, commonly called silkworms. Silk is a continuous filament around each cocoon. It is freed by softening the cocoon in water and then locating the filament end; the filaments from several cocoons are unwound at the same time, sometimes with a slight twist, to form a single strand. In the process called throwing, several very thin strands are twisted together to make thicker, stronger yarn. Silk was discovered in China sometime before 2700 BC, and the secret of its production was closely guarded for millennia. Along with jade and spices, silk was the primary commodity traded along the Silk Road beginning about 100 BC. Since World War II, nylon and other synthetic fibres have replaced silk in many applications (e.g., parachutes, hosiery, dental floss), but silk remains an important luxury material for clothing and home furnishings. More than 50% of the world's silk is still produced in China.

This entry comes from Encyclopædia Britannica Concise.
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