I am not one of those people who separates my wardrobe into categories depending on the season. My winter outfits are my summer outfits and vice versa, so if I don't make some minor tweaks to my thinnest summer jeans, I'll freeze to death. The best thermal underwear can ensure that any outfit is below-freezing friendly, so whether you're looking to reinforce your favorite legging-sweater combo or bulk up for a winter hiking trip, you'll be totally set this winter.
Due to some serious advancements in the realm of winter fabrics, manufacturers no longer need to make things bulky, in order to make them warm. That means that looking like the Stay Puft Marshmallow Man on your next ski trip is something that's totally optional — and you don't even have to endure frostbite while looking especially sleek.
Fabrics like rayon and polyester help to wick moisture while retaining body heat; they're also exceptionally thin and body-hugging, so you can layer until the cows come home, while keeping your mobility up and your bulk levels down. If you're looking to cold weather-proof your favorite outfits this year, check out these great base layer and thermal underwear options that are sure to keep you extra cozy.
1This Thin Set That Retains Body Heat
Rocky Womens Thermal Long John Underwear Set (S-3XL), $19-$23, Amazon
Made from an exceptionally warm blend of cotton and polyester, this Rocky thermal long underwear set helps to retain your body heat with its lightweight but warm design. It comes with both a shirt and a pair of ankle leggings, and reviewers say that the material is soft and durable. They also come in your choice of 16 different colors, from the bright to the subdued.
2This Adorable Printed T-Shirt
Plus Sized Thermal Knit Tee (M-5X), $20-$25, Woman Within
Whether you're wearing it to bed or layering it underneath clothes, this Plus Sized Thermal Knit Tee is both adorable and extremely functional. You can get matching pants (sold separately), and reviewers are saying things like, "It fits close to the body and is therefore ideal to wear under a T-shirt or maybe under a flannel or denim shirt. It is well made, warm and the pink color looks good."
3These Silk Pants For The Skinniest Of Jeans
Terramar Women's Thermasilk Pant (XS-XL), $22-$55, Amazon
If you're looking for an insanely thin option that'll fit underneath the skinniest of jeans, then this Terramar Thermasilk pant is it. They're made from 100 percent filament silk, which both hugs your body and works to retain heat for the warmest base layer possible. They also have a generous stretch for all-day comfort, as well as an elastic waist and leg cuffs.
4Warm And Flexible For Winter Exercise
FX Fleece Compression Performance Long Johns (S-L), $17-$25, Amazon
Especially great for things like hiking and jogging, FX fleece compression performance long johns are silky smooth, but surprisingly warm. They offer a four-way stretch, which allows for optimal movement while exercising, and they're made from a sweat-wicking material that keeps you dry and warm in the coldest weather. "Warm and soft, no binding, no crawling, no sagging. I work in extreme weather conditions and I've tried many silk and/or cotton thermal under garments to stay warm and dry. Nothing compares," one reviewer said.
5This Adorable Romper That's All Over Pinterest
Moxeay V-Neck Romper (S-XL), $20, Amazon
This cozy and adorable Moxeay V-neck romper is all over Pinterest right now. While loads of people wear it around the house, it also makes for a convenient upper-body thermal that won't ride up due to the onesie design. Reviewers love the easy-clip buttons that go all the way down to the belly, so low-plunging necklines aren't an issue.
6Fleece Lined Leggings For Yoga, Lounging, Or Layering
90 Degree Reflex Fleece Lined Leggings (XS-XL), $20, Amazon
Whether you're working out, going for the sweater-and-leggings look, or wearing these under jeans, the 90 Degree Reflex fleece lined leggings are a life-saver. They've got a velvety soft layer of high-quality cozy fleece, they come in 12 different patterns and colors, and reviewers can't stop raving: "Best purchase I've made all year," and "I wish I could order 5 more pairs. These are AWESOME."
7Tons Of Warmth Without Any Unecessary Bulk
32 Degrees Heat Scoop Thermal Top (XS-XL), $15, Amazon
Ideal for layering because of how thin and form-fitting it is, the 32 Degrees heat scoop thermal top has a great mix of fabric that includes rayon, which is extremely soft and moisture-wicking. It comes in a whole bunch of adorable colors and patterns, won't add any unnecessary bulk to your winter clothing, and is super easy to take care of: Just throw it in the washer alongside the rest of your clothes.
8Fit For The Great Alpine Wilderness
Minus33 Merino Wool Women's Crew (XS-3XL), $64-$104, Amazon
Made with 100 percent Merino wool and ideal for the coldest of climates, this Minus33 Merino wool crew has an exceptionally warm base layer, interlock knit construction, and flat seams to prevent chafing. "I've spent a lot of very cold, miserable winters wearing other 'thermals' that either didn't help at all or made me sweat so much because they did not breathe," says one reviewer, who broke these in on a camping trip in the great alpine wilderness. "I literally lived in these things and wouldn't hesitate to buy another set."
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