Capilene Expedition Weight is indispensable as a base layer for extreme conditions. It also makes an excellent midlayer. Sized for an against-the-skin fit; buy a size up if you intend to wear them loose.
Very long lasting and versitile. Can be used in most conditions due to its excellent breathing. Used in conjunction with a wind shell keeps you very toasty. With fleese pants and wind shell a bombproof summit apparel. On its own keeps you out of the sun without letting you overheat.
It didn't take long for me to fall in love with my Patagonia Capilene Expedition Weight underware bottoms. I wore them while hiking to the summit of Telescope Peak in Death Valley. It was one of those early May days where one moment and one location was warm, then a little later and further along, it was cold. I didn't have any problems with sweat, they wicked well. My legs were warm the whole time, even in the wind.
I have a 15 degree sleeping bag (which the temperature was close to that night). I slept in the bottoms, and my legs felt just right. I look forward to using these in future cold weather treks.