INSTRUCTIONS
During times of intense physical exertion, dressing too warmly can actually make you feel cold. The perspiration is unable to escape and therefore remains in constant contact with your skin. It is therefore useful to have a liner jacket that you can remove in more mild temperatures. It's also important to open the vents before you get too hot and close them before you get cold when the intensity of your physical effort decreases, as it does on the ski lifts.
What should you wear under your ski trousers?
To keep warm and dry, use the 3-breathable-layers rule: 1 breathable skiing base layer, 1 liner jacket to retain the warmth and 1 ski jacket to protect you from the elements.
The first layer
This keeps you dry by wicking away the perspiration from the skin to the other layers.
The second layer
To provide warmth, you need to wear a second layer that insulates you from the cold. This function can be provided by a pullover, fleece or padded jacket.
The third layer:
Protection from the outdoor elements (snow, rain and wind) by preventing them from entering (while still allowing perspiration to escape so that you do not feel "wet inside"). It should therefore ideally be waterproof and breathable. The third layer can also provide insulation in the case of lined trousers or jackets. This complements the properties of the second layer.