Layering your clothing is a tried-and-true way to maximize your comfort in the outdoors. The beauty of this simple concept is that it allows you to make quick adjustments based on your activity level and changes in the weather.
Each layer has a function. The base layer (against your skin) manages moisture; the insulating layer protects you from the cold; the shell layer(outer layer) shields you from wind and rain. You simply add or subtract layers as needed.
For outdoor comfort, your base layer should be made of merino wool, synthetic fabrics such as polyesters. A base layer can be anything from briefs and sports bras to long underwear sets (tops and bottoms) to tights and T-shirts. It can be designed to fit snugly or loosely. For cool conditions, thermal underwear is available in light-, mid- and expedition-weights. Choose the weight that best matches your activity and the temperature.
The middle layer serves the purpose of insulation by trapping heat closer to the body. Natural fibers such as wool, goose and fleece garments work best in such situations.
The shell or outer layer protects you from wind, rain or snow. Shells range from pricey mountaineering jackets to simple windproof jackets. For monsoons, it is required that you carry a raincoat.