Stay away from cotton, as it is not a good insulator and once it gets wet, its wet for hours and hours. I have a lite weight polyester type blend as my base layer and a set of polar weight double fleeced mtp's from cabela's as my top layer when its in the 20's. You can wash these and then hang them up and they'll be dry in less than an hour. You want something that will wick moisture away from your body and will dry quick. Just because something keeps you warm at work, remember, at work your moving around, not sitting absolutely still in a metal stand for hours.
