I've had several pairs of these combination cotton/poly long johns, and am very satisfied with them.  I bought them primarily for the moisture wicking properties. I have tried pure silk, but these tend to wear fairly quickly and perhaps only last a winter or two.  The combination of cotton and poly makes these more durable, with no seams coming loose or evidence of wear.  They provide a nice comfortable base layer in cold climes, can be worn indoors and out, and make great pajama bottoms as well.  If you are purchasing these for mainly indoor (winter) use commuting, etc., then consider a higher poly/silk content, as these (60% cotton) do get quite warm indoors.  Pure silk drawers work the best indoors, but they will also wear quicker, seams will fray, and they cost considerably more too.  If you are 6'4 or taller, get the "Tall" size.

konedog