Silk is a natural "protein" fibre which comes either from bombyx butterflies which produce cultured silk, or from free-ranging caterpillars which produce wild silk.
The caterpillar spins a cocoon in which it will transform into a butterfly. Before the cocoon appears and emerges, it is smothered with water vapour or poisonous gas. The thread can then be recovered. At first glance, this material might seem environmentally friendly because it is natural, biodegradable and renewable. However, like all intensive farming, silkworm rearing has a negative ecological impact. It involves the use of chemicals, pesticides and fertilisers, which are harmful to the planet, but also to the workers. It also puts animal welfare at risk, as the recovery of the silk requires smothering the cocoons in ovens at 80°C. After treating the worms with antibiotics and hormones, they are scalded to kill the chrysalis without damaging the cocoon, which requires a lot of hot water. Lyocell (or TencelⓇ) is preferred as an alternative.