Silk, the most valued of all fabrics, makes an excellent clothing because it is soft, light weight, long lasting, and can be dyed in brilliant colours.
Sericulture is the process of raising silk moth and harvesting their cocoon to obtain silk fibres. There are several species of silk moth and they feed on different types of leaves, that's the reason why silk can have different characteristics.
When the eggs hatch into larva, it began to feed voraciously on leaves. They shed their skin four times during this stage. After a period of 4-5 weeks, the larva spin their cocoon. Cocoon is fibre which is made from all the leaves they have been ingesting mixed with saliva.
It takes about a week to complete the cocoon. Once cocoon is complete moths are killed before they emerges. If moth will break the filament it makes reeling difficult and produce a low grade of fibre. So in order to keep the cocoon intact, they are put into containers of hot water. This kills the moth and also loosen the filaments. Now the filaments from several cocoon are reeled together to make a strong thread.
About 2000 moths are killed to make just a pound of silk, which is probably the reason to make it so expensive. Imagine an industry which strives on killing living beings.