In choosing the right clothing there is one material you want to avoid at all costs and that's COTTON.
The main purpose of clothing is to provide some type of insulation or barrier between your body and the outside. Clothing keeps you warm by trapping warm air near your skin. When cotton gets wet, it ceases to insulate you because all of the air pockets in the fabric fill up with water. When you hike, you perspire, and any cotton clothing touching your skin will absorb your sweat like a sponge.
In addition, wet cotton does not wick water away from your skin. Wicking fabrics move water from wet areas to dry ones using a process called capilary action. For example, a wicking baselayer shirt made out of Patagonia Capilene will move moisture from the surface of your skin to the outer layers of your shirt leaving the part of the fabric touching your skin dry. This is why layering is such an effective clothing strategy for hiking, because wicking fabrics move water away from your skin and up through your layers one after another, enabling the fabric near your skin to trap insulating air and retain your body’s warmth.
Avoid wearing garments that are labelled as corduroy, denim, flannel, or duck. These are all made with cotton. In addition, steer clear of cotton-polyester blends, for example 50/50. They’ll still kill you, although it may take a little longer.
Additional Resources: REI’s How to Choose a Baselayer is a good source of additional information on the comparative strengths and weakness of different fabric types, and provides a good list of clothing synthetic and wool clothing manufacturers.
courtesey of www.sectionhiker.com