Permanent press refers to fabrics that have been chemically treated to stay wrinkle free. The permanent-press washer cycle minimizes wrinkles by spraying clothing with water during the spin cycle. The permanent-press dryer cycle helps clothes stay wrinkle free with the application of medium heat followed by a cool-down period.
Wrinkles form when water breaks the chemical bonds that hold fabric fibers in position. Early permanent-press fabrics were treated with formaldehyde to strengthen the bonds, but the formaldehyde also caused problems including yellowing, itchiness and odors. Chemicals such as dimethylol ethylene urea make the bonds waterproof for better wrinkle resistance without changing other properties of the fabric.