The Rule of 3
In the mountains, the rule of 3 becomes a golden rule for clothing. You should wear at least 3 layers of clothing, but these should be chosen carefully.
The first layer, in contact with the skin, should be breathable in order to wick away sweat and thus reduce moisture. The second layer should trap in warm air, in order to create a temperate middle section. The third and final waterproof layer should protect the body from the elements such as water and wind.