Silk is a natural fiber made by the silk worm larvae. Silk is often used to make cloth. The cloth can be made into clothes, rugs, bedding, or can be used to write or paint on. Silk fibers are very strong. In the past, silk was used to make parachutes.
In history, silk came from China and was very expensive.
Most spiders make a natural fiber that is also called silk.
Silk that is emitted by the silk worm consists of two main proteins, sericin and fibroin. Fibroin is the structural center of the silk. Serecin is the sticky material surrounding it. Fibroin is made up of the amino acids Gly-Ser-Gly-Ala-Gly-Ala and forms beta pleated sheets. Hydrogen bonds form between chains, and side chains form above and below the plane of the hydrogen bond network.
The high proportion (50%) of glycine (which is a small amino acid) allows tight packing. Tight packing makes the fibers strong and resistant to breaking. The tensile strength is due to the many interseeded hydrogen bonds. When silk is stretched, the force is applied to these many bonds, and they don't break.
Silk is resistant to most mineral acids, except for sulfuric acid, which dissolves it. Perspiration makes silk yellow.