The main purpose of Ski Pants are the same as for any piece of outdoor apparel: to keep you warm, dry, comfortable, and well protected against bumps, scrapes, and other outside force. The Three Layer System is generally accepted as the best way to maintain your Thermal Equilibrium and protect you from cooling off too much. In short: the first layer, or base layer, is the only layer in direct contact with your skin and its main purpose is to 'wick' moisture away from the skin. The second layer, or insulation layer, is also meant to transfer moisture away from the body but is mostly responsible for insulating your body by trapping body heat. The third layer, or outer shell, is the layer in direct contact with the outside environment. It should be water- and windproof while at the same time being able to breath to allow body moisture to leave. For more information read out article on the Three Layer System.