Silk is natural protein filament produced a caterpillar of butterfly - silkworm. It is a strong, soft thread neither phytogenous nor animal which is produced by a caterpillar before turning into a pupa (chrysalis).
Silkworm is the most widespread insect-manufacturer on the Earth. It produces filament for taffeta, atlas, sateen, organza, and chiffon.
The noblest (and most expensive) silk is reeled off not boiled, its thread is pulled out from inside the cocoon.
To receive 3 kg of silk thread it is necessary to provide caterpillars with leaves of approximately 30 mulberry trees.
Artificial silk was invented only in the 19th century; before that only natural silk was used for fabrics manufacturing.