I hunt in December in northwest lower Michigan. Some of my hunts are in 10° weather with some wind. Battling the wind is the tougher gig over the base layer in my opinion. I have used smart wool, silk and Craft (cross country ski racing designed long underwear) base layers and they are all good. The real key for me was getting the outerwear right. I use Gray Wolf Woolen wool, lined with their windblocker material in my bibs and the wind block combined with comformax insulation in a 1/2 zip pullover. I can wear a couple of very light layers under this and stay on a December tree stand sit for four hours in about any weather. If I had it to do all over again I would just get the wind block liner in the pullover so that I could use it in more weather opportunities then just super cold.