The Three Layer System for Hiking Clothing

• The "Base" layer should consist of thermal underwear. T-shirts and such don't work for the base layer, because they retain moisture, which doesn't cool you off after you sweat. Thermal underwear makes a better base layer for hiking clothing because it doesn't stay wet, and it transfers the moisture away from your skin, so you cool down quicker. Fabrics should be lightweight and durable.
• The "Insulation" layer comes next. It helps retain body heat by creating a dead layer of air around your body. Fabrics should be warm, such as fleece or pile.
• The final layer is the "Outer Shell," which consists of a lightweight nylon or other shell, usually with a hood. This layer protects from wind, rain, and helps get rid of body moisture.