The name silk is thought to have originated from the greek word seres. In Old English, silk was sioloc. Most of the worlds silk is derived from the cocoons of the moth Bombyx mori which lives exclusively on the leaves of Morus alba, the white mulberry tree. There are other species of silkworm but their contribution to world silk is small. One cocoon is made of a single silk thread between 300 and 900 metres long. A silk strand consists of two silk filaments encased by a protein called sericin. The sericin can be dissolved in mild alkaline leaving the pure silk threads.

Their are similarities in the structure of silk and wool in as much as both polymers are proteins composed of amino acids, the general structure of proteins can be found here. It is interesting to note that the peptide group in silk (and wool) is identical to the amide group found in nylon. Chemically, both silk and nylon are polyamides. It was in part the polyamide nature of silk which directed the research which led to the synthesis of nylon (nylon was designed to replace silk as a synthetic textile fibre)

The silk polymer is a linear molecule composed of the protein fibroin. This protein is composed of sixteen amino acids of which three - alanine, glycine and serine - constitute 80% of the polymer. There are no amino acids containing sulphur in fibroin and so no disulphide bonds. The silk polymer system is about 65-70% crystalline giving a high tensile strength to the fibres.

Acids can degrade silk fairly easily since once the peptide groups are hydrolysed there are no disulphide bonds (as are found in wool) to hold the structure together. Alkali causes the silk fibre to swell. Prolonged exposure to alkali results in the complete degradation of the polymer structure.