Why Cotton Is a Poor Choice in Cool, Wet Weather
Cotton is comfortable around town, and on hot, dry days it can even help you stay cool. In cool, damp or windy conditions, though, wet cotton pulls heat from your body quickly. Understanding why helps you choose clothing that keeps you safer on the trail.
What happens when cotton gets wet
Cotton fibers absorb a lot of water and dry slowly. Once soaked by sweat or rain, the fabric loses most of its insulating value and clings to your skin, and evaporation from it draws heat away from your body.
Add wind and a rest stop, and a pleasant hike can become a situation where hypothermia is a real risk, even well above freezing.
Better fabric choices
Synthetic fabrics such as polyester absorb little water and dry fast. Merino and other wools stay warmer when damp and resist odor. Both make good base layers and socks for most hiking conditions.
Jeans are a common example of a poor choice: heavy, slow to dry and cold when wet.
When cotton is fine
On hot, dry days, a cotton shirt that holds sweat can actually feel cooler. Cotton is also fine for sleeping clothes at a car campsite if it stays dry in your bag.
The key question is whether you could get wet and cold far from shelter; if so, leave cotton at home.