Washing and drying the fabric can shrink it, but only a bit. As a synthetic fabric, polyester doesn't shrink much, but when it's blended with a natural fiber such as cotton, expect more shrinkage.
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Washing the Clothes
When washing polyester with the intent to shrink it, use a hot water wash and rinse cycle if possible. In most cases, the water in your washing machine doesn't get hot enough to shrink 100-percent polyester, which requires temperatures above 140 degrees Fahrenheit to shrink. But with polyester and cotton blends, the hot water starts the shrinking process by causing the cotton fibers to constrict.
Drying the Clothes
The clothes dryer circulates hot air around clothes to evaporate the moisture, providing an effective way to shrink polyester fabric. Use the hottest setting for the maximum amount of shrinkage, although 100-percent polyester doesn't shrink significantly. Ideally, the air inside the dryer should reach 180 degrees F or higher. When drying clothes made of a polyester and natural fiber blend, the hot air shrinks the garments more effectively.
Using Boiling Water
For noticeable shrinkage to occur in polyester clothes when wet, place the clothes in boiling water. The heat of the water breaks down the fibers slightly, causing them to shrink. More shrinkage occurs with polyester and natural fiber blends than with 100-percent polyester. The necessary boiling time varies depending on the clothing's size and the thickness of the fabric's weave, but in general, boil the clothes for about as long as a normal washing machine cycle -- often about an hour.
Ironing isn't an ideal way to shrink polyester, even when working with damp fabric; finding the right temperature that shrinks an area without melting it is too complicated. Polyester is wrinkle-resistant, so pulling it out of the dryer as soon as the clothing is dry typically reduces the need for ironing. If you must iron polyester, use a low or medium setting; higher settings melt spots in the fabric, ruining the garment.