Shrinkage of cotton T-shirts is a common phenomenon that occurs due to the unique structure of cotton fibres. Cotton fibres consist mainly of cellulose, a natural biopolymer. ‘Biopolymer’ means that cellulose is made up of long chains of glucose molecules, one attached to the other to form strong rows typical of almost all plant cells. In cotton, long filamentous cellulose molecules intertwine into lattice structures reminiscent of the hash mark (#) on a smartphone keyboard.
This lattice tends to swell when wet and contract when dry. This process of swelling and shrinkage is what causes cotton clothes to shrink. The weaving of cotton fibres to make clothes creates a network of bonds between the cellulose molecules. When washed with water that is too hot, this network of bonds can transform, causing the fabric to relax or contract. The amount of clothing shrinkage is determined by a number of other factors, including the type of detergent used, the drying temperature and whether the clothes had already shrunk. Synthetic fabrics, such as polyester and nylon, are more resistant to shrinkage because their tightly woven, waterproof fibres do not swell in water. Cotton clothes can be re-stretched using a steam iron, which reintroduces moisture into the garment to expand the fibres while applying mechanical force to stretch them again. However, this method can easily lead to overstretching the cotton, so it is important to proceed with caution.
