Cotton has been used as a primary component of clothing for at least 7,000 years. Today, it is used in a majority of conventional attire, such as denim jeans. It is important to know what water temperature to use when cleaning cotton, as high temperatures will often alter its size.
Washing a cotton product in hot water can and often will cause it to shrink. This is known as shrinkage. As a result, tight-fitting clothes should not be exposed to hot water; it can make the clothes uncomfortable or impossible to wear. Hot water is typically used to wash products like lingerie, bathrobes, washable rugs, delicates and white clothing.
Cotton shrinks due to a process known as relaxation shrinkage. Relaxation shrinkage occurs due to the manner in which cotton is constructed and woven. When a cotton T-shirt is made, for example, the cotton fibres are stretched and woven together to create a product that is tougher and more resilient to damage. This creates a natural, persistent tension within the cotton fibres. According to cotton.org, "the tension is released when the fabric is washed or steam pressed, causing it to shrink to its natural size."
Shrinkage can create issues with sizing. For example, an individual who normally wears size medium may find that his size medium cotton T-shirt fits too snuggly after a few washes. As a result, companies that produce cotton products will often wash and dry them in advance to limit future shrinkage. This is known as pre-washing. A cotton product that has been pre-washed will typically say so on the tag next to the washing instructions.
The simplest way to avoid shrinkage is to wash cotton products in cold water (23.9 to 29.4 degrees Celsius) and hang-dry them. Hang-drying cotton products will allow them to avoid the high temperatures of a conventional dryer, which can also cause shrinkage.
If a cotton product fits too loosely, it can often be intentionally shrunk in the washer and dryer. Cotton products that have not been pre-washed will experience the most shrinkage when exposed to hot water. Pre-washed cotton products may still experience some shrinkage, but the effects of hot water on these are not as severe.