Cotton fibres are the seed hairs of the plant Gossypium. The word cotton comes from the Arabic word 'kutan'. Approximately 50% of the textile fibre demand in the world is met using cotton. It is grown in many parts of the world, the main areas being USA, Russia, China, India, Egypt, Africa and South America. Cotton is typically composed of 88% to 96% cellulose, the remainder being protein, pectic materials (carbohydrates in a 'gum' like form) and wax. Cotton must be scoured (and usually bleached) before use, which then leaves the cotton as about 99% cellulose.

The cellulose polymer of cotton is a very long linear molecule about 5000nm (nm=nanometre which is one billionth of a metre) in length and 0.8nm thick. The numerous hydroxyl (OH) groups are important for for forming hydrogen bonds between cellulose polymer chains and thereby contributing to the three dimensional structure of the cotton fibre. About 70% of the polymer system is crystalline (ordered or regular arrangement of the individual polymer molecules relative to each other)) whilst 30% is amorphous (disordered). The high crystallinity makes cotton inelastic leading to easy creasing and wrinkling of cotton fabric. Cotton actually gains strength when wet (one of the few fibres to do this) due to temporary improvements in the degree of crystallinity in the amorphous regions.

Cotton is weakened and destroyed by acids but is resistant to alkalis. Air pollutants are usually acidic and may contribute to cotton fibre breakdown through acid hydrolysis. Cotton is pretty easy to dye and print on using azoic, direct, reactive,sulphur and vat dyes.

Cotton can be mercerised which causes the fibres to swell (increase in thickness and decrease in length). This is achieved by immersing the fibres in strong alkali such as caustic soda followed by thorough washing. This imparts considerable tensile strength to the fabric and makes subsequent dyeing easier.