Cotton is one of the most absorbent materials on the market. You can witness the absorbent qualities first hand when you use a cotton ball to soak up whatever liquid it contacts. It almost magically draws the liquid up into its fibers, trapping it there. It’s not magic, however, but simple science. And understanding this science can also help you determine when cotton is an inappropriate material to use. Athletic wear, for instance, or any time you want to stay warm and dry.
Here’s how cotton works and how cotton can be dangerously ineffective.
Cotton’s Absorbent Qualities
Cotton fibers are extremely absorbent. Cotton can trap approximately 0.3 gallons of water per pound of cotton, according to the EDRO Corporation. Gizmodo claims that cotton garments can carry to up to 27 times their weight in water. That kind of absorption is staggering for such a common fabric.
Why is this the case? It all comes down to science, according to the website How Stuff Works. The basic molecular structure of cotton is perfectly attuned to collecting moisture. Water, of course, is made up of two hydrogen atoms and one oxygen atom. That oxygen atom loves to attract electrons, which gives it a negative charge. Those hydrogen atoms, however, are positively charged. This makes the water molecule a dipole, which operates sort of like a magnet, clinging to any oppositely charged molecules that come near by.
Cotton, you guessed it, is one of those oppositely charged molecules. The oxygen-hydrogen groups that line the edge of cotton’s long cellulose molecule attract water, sucking it right up into its fibers. For this reason, cotton is considered a hydrophilic material. It can’t help it. It’s always going to attract and hold on to whatever water it can, up to its enormous capacity.
Other materials, nylon for example, don’t have these same properties. It will still attract water, but there are fewer molecular opportunities for it to do so with less oxygen-hydrogen groups available. That’s why synthetic materials engineered without these water absorbing opportunities are often used for athletic wear, where dryness and breathability are key.
Hikers and backpackers have a saying: cotton kills. When you’re faced with a survival situation, cotton can often mean the difference between life and death.
“National Park employees, Girl Scouts and Boy Scouts all use the phrase ‘cotton kills’ to remind people not to wear it when in the woods for an extended period of time,” Appalachian Trail Histories says. “The main complaints against cotton are the time it takes to dry, stretching when it is wet and chafing.”
While these characteristics can be uncomfortable at any time, they become particularly dangerous in colder temperatures, which is how cotton got it’s nefarious reputation. “Getting wet in the cold is dangerous no matter what material the person wears,” Appalachian Trail Histories says, “but a fabric that retains moisture slightly increases the chance of hypothermia. Of all the fabrics available today, cotton is one of the most uncomfortable to wear when wet.”
This is a main reason that cotton is not often found in athletic clothing any longer. Your morning jog might not seem like a life or death situation, but the same principle applies. There’s nothing more uncomfortable than the feeling of your athletic clothing clinging to you during savasana after a long, sweaty heated vinyasa.
A Better Alternative
High tech, synthetic fabrics with a tight weave fare better for athletic clothing and any other time you don’t want the potential for your fabric to accrue moisture. Synthetic fabrics can be engineered to reduce or eliminate the opportunity for those molecular bonds to form that attract water to a material in the first place. A fabric made of fibers woven extremely tightly together is even better. This reduces the surface area of fibers exposed to the elements, which reduces the number of opportunities water molecules have to cling to the fabric.
In modern athletic wear, you’ll often see material that meets these needs. It’s a tighter, synthetic weave that’s meant to prevent trapping moisture in your clothing and thus against your body. This keeps you more comfortable and more able to regulate your body temperature.
Cotton is fine for some things, like removing nail polish or sopping up spills, but in any situation when it’s important to stay dry, avoid cotton materials. When it comes to bedding, find the sheets you deserve with the textiles that work for you, not against.