Whether you head outdoors for work or play, thermal underwear is your first line of protection against cold winter conditions. A first layer of long underwear allows you to customize your comfort in changing conditions by adding or removing outer layers. And is there anything more relaxing than chilling out inside on a cold winter night in a fleecy, thick pair of long johns? Just add hot cocoa, and you may never leave the sofa. Check out our guide to the best long underwear for any activity—whether you’re braving the cold or hunkered down by the fireplace.