I sweat a lot when hunting and for the past 20+ years I have stayed away from cotton as a base layer. I have several pieces of the Cabelas Thermax long underwear in different weights and the stuff has been fantastic. They don't make Thermax brand anymore but there is similar products out there including Under Armour. When it's warm I wear an Under Armour t-shirt under my hunting shirt to absorb the perspiration. When elk hunting in the cold and snow I use nothing but a heavier weight Thermax as a base layer with nothing but Wool on top. Wool pants, shirt and parka. There is nothing made that can beat wool in cold and snowy conditions. Especially when you sweat like I do because it "Breathes". Unlike the GoreTex type products. Back in the mid 90's I was hunting elk in Colorado. It was very cold and a lot of snow. The guy I was hunting with has the Browning Big game bibs and parka insulated and GoreTex lined. We worked up quite a sweat climbing one mountain in the morning. I stayed warm and toasty in my Wool but he was soaked underneath and by the end of the day he had Hypothermia. He was one sick dude for the next couple days.
Mu suggestion for upland and big game hunting where you are moving alot: Stay away from Cotton and GoreTex. You need clothing that will breathe and dry quickly.
Agree w/ all the above, there's nothing better. I bought lots of it at the factory outlet in San Marcos. They have some unbelievable sales on good stuff.
I have hunted chukars in steep country when it was 0 to 15 above with just a base layer of Thermax and my bird vest. I often start with a layer of UA or fleece over it and then take it off and put it in the vest. Same for elk hunting, wool pants over a layer of UA on the bottom. Amazing how warm and dry you can stay as long as you are active with limited clothes. I still hunt with a few folks that don't believe in new flanged clothing, at the end of every day they complain they are 'wet' while removing cotton baselayers. LOL!
I hate anything that fits like a hot dog skin. Never could ware turtle necks or other tight fitting clothes. Under Armor is that type of clothing.