We sent 13 testers out in the winter to hike, ski, shovel snow, and run, and we found a variety of styles, fabrics, and cuts that will keep all types of bodies warm. We have picks that will take you from city to trail, picks for hiking and backpacking, and picks for fishing and hunting, or even for skiing and snowboarding. We also have options for getting muddy at sports practice or for layering under your civilian clothing. And of course we have a budget option.
In the title of this guide, we call these layers “thermal underwear” because that’s what most people search for when they’re looking for something to be active in. And that’s what base layers are—they don’t just keep you warm, they also regulate heat. If you’re looking for loungewear or pajamas, we have a guide to those, too.