Long johns, thermal underwear, or base layer bottoms are thermal underwear worn for two purposes–to keep you warm, and to keep you dry. They probably got their name from the boxer John L. Sullivan who wore them in the ring.
Long johns come in many variations for a wide range of purposes anywhere from expeditionary mountain climbing to watching a late fall football game.
To learn more about thermal underwear and how to choose the best pair for you, take a look at our buyer’s guide for all of the details, and our top picks across the different categories.