merino woolDon't wear synthetics. The keep you hot in the lodge and chilled on the lift. Merino wool as a base layer and any wool as a mid layer is best. The mid layer is less critical. Icebreaker, Smartwool and Ibex make great products. Other wools work as well but itch more. If the pure merino bothers your skin use Outdoor Research's blend. Alpaca wool may be the itchiest, even as a mid layer.
Never wear down on the slopes. I bought a down coat and after 200 yards was already sweating. Fine for walking around town.
Skiing at Jackson Hole last year it was -8. I wasn't cold skiing or on the lift and wasn't hot in the lodges yet I'm slim with little body fat.
Capilene is the best synthetic but just isn't close to wool.