I used to always feel cold in the winter until I discovered Wintersilk long underwear pants.
"Whisper-fine silk forms our most popular men's long underwear. Warm & breathable to protect you from the elements. Airy & light for comfort indoors and out. They're perfect as cool weather sleepwear. And thanks to the hard-wearing characteristics of natural silk, you can toss them in the wash and expect them to last for years."