It’s happened to the best of us: without thinking, we throw a new cotton shirt in the dryer, and voilà: we now have a shirt suitable for a toddler.
Cotton is prone to these types of washing errors in a way that synthetic fibers, such as polyester, are not. Much of this vulnerability comes down to the individual fibers of the cotton clothing, Jillian Goudfarban associate professor of chemical and biomolecular engineering at Cornell University, told LiveScience in an email.
“Cotton fabric is made by weaving together fibers from a cotton plant, which themselves are largely made of cellulose, a natural biopolymer,” she said. “Cotton…is prone to shrinkage because the fibers swell when they get wet and then contract when they dry.”
If you’ve ever sweated in cotton clothes, you know firsthand how well they can absorb moisture. On the other hand, synthetic fabrics, such as polyester, nylon and spandex, are more resistant to sweat and shrinkage because their tightly woven fibers do not swell in water.
Chemically, weaving cotton fibers for clothing introduces stresses that create a network of hydrogen bonds, Erika Milczek, a chemist and CEO of a biotechnology company CurieCotold LiveScience.
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When variables such as heat and water are introduced, this hydrogen bond network can transform, causing the substance to relax or contract. This is also the science responsible for wrinkles in your clothes, Milczek said.
The science of shrinking
When it comes to accidentally shrinking your cotton clothes, not all items are created equal, Goldfarb said.
“Even if they are made of the same material, some cotton fabrics are more susceptible to shrinking than others, depending on how the fibers are put together into a fabric,” she said. “Woven cotton, while it will certainly shrink, shrinks significantly less than knitted cotton.”
Imagine the intersection of woven cotton fibers, like a hashtag, with some fibers being woven among others, Goldfarb said. Horizontally woven yarn is called the “warp”, and vertically woven yarn is called the “weft”.
“As the yarns swell when wet, they push the wefts closer together, causing them to shrink in one direction,” Goldfarb explains. “When the moisture is removed from the fabric, the fibers contract.” This means that shrinkage actually starts before the clothes ever go into the dryer. Shrinkage is the dual consequence of water-retained fibers and high heat.
Exactly how much your clothes shrink is determined by a number of factors, Milczek said. For example, it depends on whether you wash your clothes only in water or add detergent (detergent disrupts hydrogen bonds even more) and whether you dry your clothes at a high or low temperature or hang them up to dry.
“The temperature [when line drying] is significantly lower, so evaporation occurs much slower and the fibers are not ‘stressed’ by the heat during shrinking,” Goldfarb explains. A line-dried shirt also experiences more consistent humidity between the outside air and your closet, which can result in less shrinkage, she said.
Storing a shrunken shirt
For some, this knowledge may come a little too late. But do not worry; there may still be hope for your shrunken garments.
An obvious answer, Milczek said, is to start by looking for clothes that are shrink-resistant. These include cotton clothing with synthetic blends or cotton clothing that has been pre-shrunk.
If that doesn’t help, there is a science-based way to try to ‘unshrink’ your clothes.
“Depending on the quality of the yarn and weave… if we swell the fibers and let them dry under tension, it is possible to ‘unshrink’ some cotton fabrics, at least temporarily,” Goldfarb said.
One way to do this at home is to use a steam iron, she said. This reintroduces moisture into the garment to expand the fibers while applying mechanical force to stretch them again. But be careful: this method can also easily swing too far in the opposite direction.
“It is of course easy to ‘overstretch’ your cotton in this way, and if it is done unevenly you can be left with a rather warped garment.” Goldfarb said.