These have been my secret to cold northern winters for years now.  I had accidentally purchased a pair of heavyweight lazys about a year ago and marveled at how, unlike the regular ones, they don't pill;  so I decided to upgrade to all heavyweight.

Sadly, the new ones are so slimfitting, I cant even kneel down without a wedgie.  No, I didn't gain any weight and when I compared the original heavyweight to the new one (measured length, arms, legs and width across chest and hips of both the old and new), it was about 20% smaller in every way. So now Im sad cause they aren't comfortable anymore; and I cant exchange them because, like all new clothes, they were washed before wearing.