when i took my hunting couse back in 76 they told me the phrase- cotton kills. once it gets wet it has no real insulating properties. all my favorite gear is wool. i like to use expedition weight polypropolene long underwear but found that it only wicks to a point. i have done some long hikes in to my stands and have found that once you get sweatty your done no matter what your wearing. its hard to convince yourself to wear something lite on the walk out to your stand when its 20 degrees but its worth it. if im carrying a stand and a pack i wear a light shirt because you will sweat on a long walk in the woods and when i get to my area i strip off the shirt and put on the insulated underwear and a wool sweater over that.you feel like your in heaven at that point. be careful of those heat packs. i have a nice burn mark on my foot because one broke open and i didnt realize it.the company that makes the heat packs also makes a lite mesh vest with pockets to put the heat packs in so your back is nice and warm.just ordered it for 20$. that should keep me warm all day.