Silk
50-65 usd/kgSilk is a natural protein fibre produced by silkworms. Used for millennia, it is prized for its lustrous surface and excellent dyeing characteristics. The filaments, up to 1,500 m long, are fine and strong.
Most of the worlds silk comes from China and India. And almost all of that is from the domesticated Mulberry silkworm (Bombyx mori). Silk production, known as sericulture, has been practiced in China for millennia and as a result, the moths have evolved to be entirely dependent on humans for their lifecycle – they are blind, mostly flightless and have lost their camouflage. There has been a great deal of genetic engineering and many hundreds of strains exist.
Production starts with the Mulberry tree, which provides the leaves that are fed to the worms. One of the largest impacts is the cultivation of the leaves, which requires pesticides and irrigation. The other half of the impacts are from housing he silkworms, boiling (to kill the silkworm) and unwinding of the silk filament from the hardened cocoon. The silk filament is held in place by sericin, a strong protein, which is heated in water to break it down and allow the fibre to be separated.
It takes around 10 kg of cocoons, which is around 2,500, to produce 1 kg of silk. In addition, composting the waste from production can have a big impact on overall CO2 emissions. Therefore, by incinerating the waste for energy recovery, the CO2 emissions can be dramatically reduced. Nevertheless, the negative environmental impacts of silk production are quite extreme.
Tussah silk, also tussore silk, is produced by several species of silkworm that are either domesticated or living wild in the forests (wild silk). Examples include eri silk (Samia ricini) and muga silk (Antheraea assamensis). Whereas eri silk is off-white and looks more like cotton once converted into fabric, muga is natural bright golden coloured.
If the silkworm is allows to complete its metamorphosis and hatch into a moth, then the cocoon is broken. In this case, it may be referred to as peaceful silk, or vegan silk, because the worm and moth are unharmed. The fibre from these cocoons can be turned into staple fibre suitable for textiles, but is not as desirable as continuous filaments from unbroken cocoons. It may be blended with other fibres to impart some of the strength and softness of silk.
Cruelty free alternatives to Mulberry silk include synthetics, such as polyamide (PA), nylon, and regenerated cellulose (viscose, lyocell, acetate), which can be produced with the same lustrous appearance and fibre cross-section. They are much less expensive, more sustainable, and their properties are highly tailorable. Plastic free options include cotton and the bast fibres, such as hemp and flax (linen). However, these materials behave quite differently.