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 are not designed to keep you warm, but to keep you from getting cold. So you need to think in reverse logic.
So base layers are designed to keep you warmer, but 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.
Looking at the different fabrics that thermal underwear/insulated underwear/base layers are made of you can easily see by the properties of those fabrics which ones are the best for outdoor adventures in the heat or cold.
Cotton – absorbs sweat well, but dries why to slow.
Polypropylene – absorbs sweat well, but retains body odor after just a few hours.
Polyester – absorbs sweat well, dries fast, great mobility, does not hold up over time.
Merino wool – hydrophilic, dries faster than Cotton, natural antibacterial properties (no odors). This is definitely the best overall fabric on the market for Thermal Underwear (Base Layers).
*Recommendation, when you are enjoying the Outdoors do not cut corners by buying something cheaper that you will not be happy with. Spend a few more dollars and get the best. Below is the Best Thermal underwear for 2021!
2021’s Best Thermal Underwear (Base Layers) for Women.
#1 Icebreaker
Icebreaker Merino Mens 260 Tech Merino Wool Base Layer Long Sleeve T-Shirt & Leggings
The Merino 260 Tech is a midweight fabric that fits comfortably next to your skin and provides great temperature regulation. The base layers are soft, breathable, resistant to odros, and fit to your body like they were made for it.
Made with 100% merino wool they are perfect for cold weather layering and ideal for Hunting, Hiking, Biking, and Skiing. The top shirt is designed with Gusseted underarms, forward side seams and offset shoulder seams to improve range of motion and prevent chafing when you’re moving fast or wearing a pack.
#2 Oasis 200
Icebreaker Merino Men’s 200 Oasis Merino Wool Base Layer Long Sleeve Half Zip & Leggings
Icebreaker 200 Oasis is made from 100% merino wool. These base layers are designed With flatlock seams to prevent chafing and gussets for comfort & mobility. They are excellent for wearing under any mid and outer layers for the ultimate cool weather adventures.
Merino is lightweight, soft, breathable, naturally odor resistant, and helps regulate your body temperature in cold or hot weather .
#3 Intraknit 200
Smartwool Intraknit Merino 200 for Men
The MERINO 200 is crafted with 53% Merino Wool, 45% Polyester, and 2% Elastane. Designed with 3D mapping you get a near custom fit, freedom of movement, and enhanced comfort.
The lightweight 200 base layer fabric is soft 100% Merino wool made with an interlock knit, which is breathable, odor resistant, and provides thermoregulation. A perfect base layer for skiing, hiking, or an all day hunt.
#4 MERIWOOL Heavyweight 400g
MERIWOOL Mens Base Layer 100% Merino Wool Heavyweight 400g Thermal Shirt & Pants
Men’s 400g/m² merino wool thermal pants and crewneck top are 100% all natural superfine 18.5-micron Merino wool, ensuring comfort and warmth for any hunting, hiking or other outdoor adventure.
The 400g Heavyweight base layers are made for all day comfort and for keeping you warm in extreme conditions.
#5 Alpine Onset
Outdoor Research Men’s Alpine Onset Crew (shirt) & Bottoms
The Alpine Onset base layers are nature’s best temperature regulating fabric. With the ability to hold onto heat in cold temperatures, manage moisture, and dry quickly, these base layers are the number one choice for any outdoor activist.
Each Alpine Onset base layer is crafted with 83% Merino Wool, 12% nylon, and 5% spandex for extra mobility. Designed for easy layering and efficient temperature control during any hunting, hiking, or biking trip.
