Thermal underwear refers to a type of clothing that helps keep the body warm by trapping heat close to the skin. It is worn underneath regular clothes during cold weather to provide extra insulation and ensure comfort. Full definition
While I have not yet tried this option, many travelers swear by silk thermal underwear during cooler or transitional seasons. (unefemme.net)
Whether you're into skiing, hiking, or you work outside, the best thermal underwear will keep you both warm and dry, which is crucial. (testfacts.com)
If you suddenly conjure up images of old ladies wearing thermal underwear, I'm pleased to say that thermals have moved a long way since then. (petitestyleonline.com)