Silkworm caterpillars secrete silk as a liquid protein called fibroin. This stiffens into a solid filament on contact with air. The caterpillar glues this into a cocoon, using a different sticky protein, called sericin.
But before the caterpillars get a chance to turn into moths, silk farmers boil the cocoons in water to kill the caterpillars and dissolve the sericin coat.
The boiled cocoons are combed until the loose end unravels and then the thread is fed onto spools and spun.
It takes five to ten silk fibre strands to make a single thread and 6,000 caterpillars to manufacture a single kilogram (2.2 pounds) of silk.