Military Saints fans--need some advice

I know we have a lot of current and former military on the board. My nephew is going to Afghanistan in January, and I wanted to give him the best, warmest, lightest, strongest--you get the picture--long underwear I can find for Christmas.

Those of you who have been in cold climates--what's the best?
That depends on what he does. Something good for a mechanic might be too bulky/ restricting for someone in combat arms.