On a moderately serious note, I've used merino wool undies and they kept my bits warmish in temperatures below minus 50. They were very comfortable even though I kept the same ones on for a month. 
__________________ "I feel unusual.." Withnail and I "A lot of people attack the sea. I make love to it." Jaques Yves Cousteau "The sea once it casts its spell, holds one in its net of wonder forever." Jaques Yves Cousteau |