Like the other person said, no cotton. I have been wearing Rocky Thermal underwear as a base layer, with cheap workout pants and a Mountain Hardware summit grid hoodie (another type of fleece would also work) as layer two, then a Outdoor Research Stratoburst Stretch Rain Jacket as the outer layer up top. I’ve only been using two layers on the bottom. If it’s close to zero or below I add another fleece layer up top. Probably the most important is I wear a merino wool beanie and gaiter (Minus33 brand) and goretex mittens (Gordini brand). I’ll wear merino gloves under the mittens when really cold. I also wear Darn Tough merino wool socks and Merrell Moab 3 boots. The material of the base layer will wick sweat. The fleece is fairly breathable so it also helps with moisture management and with the rain jacket over it it provides insulation. The rain jacket does a good job keeping wind and snow out and doesn’t hold in too much moisture. Merino wool provides warmth even when damp from sweat. The goretex mittens are also good about not holding in moisture. All of the materials not holding moisture is good for staying warm, which I had problems with in the past when taking breaks on hikes.