Wool or poly as a base layer. I have used both and like the Merino wool for it doesn't itch, and does a good job keeping my skin dry. Merino wool is marketed by one company as "SmartWool". I have been able to find Merino wool sweaters in thrift stores for $3-$5 and buy the bottoms at local sporting goods stores. A tip- when walking to your stand/blind walk in with your hat off and upper layers open to keep from sweating.