Silk fiber is a continuous protein filament produced by a silkworm to form its cocoon. The principal species used in commercial silkmaking is the mulberry silkworm (the larva of the silk moth Bombyx mori) belonging to the order Lepidoptera. The raw silk fiber has three elements—two filaments excreted from both of the silkworm’s glands and a soluble silk gum called sericin, which cements the filaments together. It is from these filaments that the caterpillar constructs a cocoon around itself.

The process of silkmaking starts with raising silkworms on diets of mulberry leaves for five weeks until they spin their cocoons. Then the cocoons are treated with heat to kill the silkworms inside (otherwise when the moths emerged, they would break the long silk filaments). After the cocoons are soaked in hot water, the filaments of five to ten cocoons are unwounds in the reeling process, and twisted into a single thicker filament; still too fine for weaving, these twisted filaments are twisted again into a thread that can be woven.