If you’ve done your fair share of hiking, camping, or general outdoorsy behavior, you might have heard people say not to wear cotton. But have you ever stopped to consider why? As it turns out, it’s not a myth. There’s a very valid reason that “Cotton Kills” is a popular saying.
The phrase, while dramatic, is an old, and quite reliable, adage for outdoor activities. Cotton is unique from other fabrics. The way that the fibers are structured allow it to not only be extremely absorbent, but to become an absolutely terrible insulator when it does get wet.
The Appalachian Mountain Club used to have an article explaining why exactly this happens. While the article is no longer available, a segment of it was saved by the Adirondack Mountain Club website.
“A cotton fiber is like a tiny tube formed of six different concentric layers. As individual cotton fibers grow on the plant, the inside of the “tube” is filled with living cells. Once the fiber matures and the cotton boll opens up to reveal its puffy white contents, these cells dry up and the fiber partially collapses, leaving behind a hollow bean-shaped canal, or “lumen”. This empty space holds lots of water.”
To put simply, cotton is essentially made up of small gaps perfect for retaining water. This allows it to hold an impressive 27 times as much water as its own weight. When you compare this to other fabrics like wool (able to soak up 0.3x it’s weight in water), it’s unbelievable.
So imagine that you’re stuck wearing a cotton sweater. Since the entirety of the material contains those micro gaps, this means that any moisture it absorbs will retain contact with the skin, as opposed to the “wicking” nature of synthetic materials. Since the moisture retains contact with the skin, it acts as a cooling layer, capable of sucking heat away from the body a good 25 times faster than when dry.
All of this culminated into a bad material for cold weather, especially when doing things outdoors. Let’s say you’re out camping for the weekend, and it suddenly rains, but all you have is a cotton sweater. If that sweater gets wet while you wear it, you’re now at a much, much higher risk of hypothermia.
So the next time you do some cold weather hiking, make a point to not wear cotton. Instead, consider alternatives like wool, polyester, and nylon. Even better, try layering them in what you find most comfortable.