A permanent press is a characteristic of fabric that has been chemically processed to resist wrinkles and hold its shape. Alternative terms include wrinkle resistant, wash and wear, no-iron, durable press, and easy care. This treatment has a lasting effect on the fabric.
The crosslinking agents that result in the permanent press finish are often derivatives of urea. A popular agent is DMDHEU, dimethylol dihydroxyethyleneurea.
Advances in producing permanent press fabrics involved a series of agents that crosslink the cellulose-based fibers that comprise most clothing. Initial agents included formaldehyde. Starting in the 1940s a series of urea-formaldehyde derivatives were introduced. Technical issues overcome included yellowing, odor, and the tendency of some agents to accelerate the degradation of fabrics by bleaches. In 1953, Brooks Brothers manufactured wash-and-wear shirts using a blend of Dacron, polyester, and cotton that was invented by Ruth R. Benerito, which they called "Brooksweave".
In older washing machines, the permanent press setting sprays moisture during the spin cycle to maintain the moisture content of the permanent press fabrics above a certain specified limit to reduce wrinkling.
Most older clothes dryers feature an automatic permanent press setting, which puts clothes through a cool-down cycle at the end of the normal heated drying cycle. Modern dryers tend to include this as a standard feature.
See also 
- Klaus Fischer et al. "Textile Auxiliaries" in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a26_227
- The development of DMDHEU is described in this news report: http://chemistry.about.com/od/howthingsworkfaqs/f/clotheswrinkle.htm
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