The cause of shrinkage explained: Heat Didn't Shrink That Shirt: Fabric Expert Offers the Scoop Saturday, November 6, 2004; Page F05 One benefit of testing Whirlpool's laundry appliances was the opportunity to talk with Lucinda Ottusch, one of the company's fabric techonologists, and demystify some of the laundry process. The first myth debunked: Dryer heat does not shrink garments. After all, as Ottusch pointed out, a hot iron does not shrink clothes; in fact, the heat and pressure of the iron cause the garment to stretch out. Rather, she said, shrinkage is caused by the tumbling action as the garments hit the sides of the dryer. Shrinkage is also caused by the washing process itself. When a garment is made, Ottusch said, manufacturers often stretch a fabric to its max so that slightly less cloth is needed. (A tiny bit of fabric factored over thousands of identical garments is a significant savings.) But when the garment is washed, the cloth fibers will shrink to their natural state. The warmer the water, the greater the reversion. If you were to put on jeans when they were wet, you would find they were too small, Ottusch said. The degree of movement of the garments during the washing process also affects the fibers, she added. As a general rule, the tumbling action of a front-loader produces less movement and fiber reversion than the agitation of a top-loader. A "preshrunk" garment has already been washed, so the garment will not be as affected by the laundering process. Compared with washing, which can shrink clothes, drying them with heat has the opposite effect. As a garment loses moisture, the fibers will stretch a bit; as you wear the garment, the heat of your body will increase this stretching. But, Ottusch said, the drying process can damage fabrics made of natural fibers such as cotton, linen and wool, if too much moisture is removed. These fibers have a natural moisture content, even when they feel dry (with cotton it's 5 percent; with wool as much as 17 percent). When the fibers are over-dried, they will reabsorb moisture from the atmosphere. The occasional over-drying will usually not cause a problem, but when it happens repeatedly, the fibers will be weakened and the clothes won't last as long or wear as well, Ottusch said. A dryer can also affect the appearance of garments. Dark ones can rapidly lose their brand-new look as they hit the sides of the drum. This raises microscopically small fibers and gives the seam areas a powdery appearance, Ottusch explained. With some types of fabric, however, the raised fibers are a plus. With a towel, for example, the raised fibers make it feel softer. -- Katherine Salant Edited to include text for those not registered with Washington Post's web site.