What is the best insulated underwear for keeping you warm? Well, first we must understand how Thermal underwear works, then we can look for those fabrics that have the best characteristics we are looking for in our base layer.
To begin, insulated underwear is not designed to keep you warm, but to keep you from getting cold. So you need to think in reverse, somewhat like a freezer. A freezer doesn’t freeze things by generating cold air, but instead removes the heat, making it colder.
So base layers will keep you warmer how? By removing sweat! So you want a fabric (base layer) that fits tight to the skin, making as much contact as possible. Next this fabric needs to be hydrophilic, absorbing sweat quickly and hydrophobic, dry as fast as possible.
Cotton – not what you want here, it absorbs sweat well, but dries why to slow.
Polypropylene – absorbs sweat well, but retains body odor and will smell within hours.
Polyester – absorbs sweat well, dries fast, great mobility, will develop odor over time.
Merino wool – hydrophilic, dries faster than Cotton, natural antibacterial properties, so no odors over time. This is definitely the best Fabric on the Market for Thermal Underwear (Base Layers).
*Recommendation, when you’re enjoying the Outdoors do not cut corners by purchasing something that you will not be happy with, spend a few more dollars and get the best. Below is the Best Thermal underwear for 2023!
2023’s Best Thermal Underwear for Men
2023’s Best Electric Thermal Underwear for Men & Women