Winters in Canada and the northern United States are no joke.
You can expect temperatures to fall well below freezing as early as November, reaching dangerously cold temperatures during the worst of the season.
And trust me, stepping outside into that weather is a recipe for getting important parts of yourself frozen off—not just fingers, toes, noses, and ears, but also those important parts (you know the ones).
Thermal underwear (formerly known as “long johns”, now elegantly called “base layers” or “thermals”) can be an absolute lifesaver.
A thermal shirt can also serve as a base layer to keep from sweating through your parka, but also keep body odor under control.
For the last few years, I’ve made it my life’s goal to find the best thermal underwear (both tops and bottoms) so I never have to suffer cold again even in the worst of winter. I’ve personally tested nearly two-dozen pairs, researched dozens more, and combed through hundreds of product reviews.
My list below features the base layers and thermals that my research proved to be most effective at protecting your most important parts during even sub-zero temperatures.
Paired tops and bottoms made from thermal (read: heavy) weight fabric that’ll keep you toasty warm even in the dead of winter. Patagonia delivers sport-ready and work-friendly thermal layers built to last for years of hard wear.
Built for long hours of walking and sweating, they’re wonderfully breathable, odor-controlling, and mobile (thanks to the gusseted crotch).
The open-grid pattern on the inside traps heat close to your skin, while the smooth outer face lets you layer sweaters or coats atop the shirt hassle-free.
Made from pure Merino wool, the Smartwool Classic Thermal Merino Base Layer Shirt is soft as a cloud but tough as nails.
The flatlock seams and lack of shoulder seams make it the perfect base layer to wear for snowboarding, skiing, or snowshoeing, and the no-chafe, moisture-wicking fabric will be comfy against your skin no matter how heavily you sweat.
Available in a wide range of colorways, it’s just a good-looking, great-feeling choice.
Pair your Smartwool Base Layer Shirt with these bottoms to complete your set. Made from the same high-quality, hard-wearing pure Merino wool, these will keep everything dry, sweat-free, and minimally odorous so you can always be comfortable even after a day on the slopes or hoofing it around town.
The heavyweight fabric offers serious insulation to keep you warm even in sub-freezing temperatures.
The Thermajohn Long Johns are some of the warmest I’ve ever tested—and I’ve tested a lot! Though only midweight, the polyester fleece fabric provides next-level heat retention and moisture-wicking properties.
The addition of Spandex into the blend makes it stretchy and flexible enough to be sport-friendly, but they’re soft enough that I can wear them for a good, long lounge session around my house, too.
Skiers and snowboarders, the Arc’teryx Rho LT Zip Neck was built for you. Lightweight breathable fabric, excellent moisture management, and maximum thermal efficiency all combine to make an ideal base layer for active guys. But even if you tend to sweat hard (like me), the Polygiene treatment ensures you smell fresh and clean all day long.
Want a base layer that you can also wear on its own? Smartwool’s quarter-zip long-sleeved shirt is my go-to.
It’s thick and structured enough it stands alone even once you take your jacket off, with eye-catching colorways that’ll pair nicely with everything from dark jeans to winter snowpants.
This is an ideal indoor choice, great for lounging by the fireplace or chilling in front of your TV or computer. The fabric isn’t odor- or sweat-proof, but it is insanely soft against your skin and beautifully comfortable for a day of rest and relaxation. Plus, the fly front offers maximum convenience when it comes time to use the bathroom.
Ridge brings its A-game with this Merino wool and nylon blend base layer. Midweight, itch-proof, naturally thermoregulating, breathable, moisture-wicking, and odor-resistant, it’s the ideal base layer to throw under a snowsuit or weekend outfit.
Flatlocked seams, raglan construction, and an ultra-sturdy fabric make this one of toughest adventure-ready base layers you could ask for. The extra length ensures it stays tucked but the quarter-zip style makes it wearable on its own.
I’m a big UnderArmour fan for their sport-friendly designs. This Long Sleeve Crew Neck is one of my all-time winter favorites. The midweight warmth makes it an ideal base layer to wear on warmer winter days, but it’s suitable even extreme cold as the first of three or four heavy layers.
Thanks to its brushed grid interior, body heat stays trapped in place so I’m warm all day—and night—long.
For fast-paced days at work, I’ll always choose my Helly Hansen thermals. Though lightweight, it does a great job of controlling moisture and odor, regulating temperature, and preventing chafing beneath a heavy work jacket or coveralls.
It’s also stretchy enough I can swing an axe, haul supplies, or scramble up ladders with total freedom of movement.
For a day spent both indoors and out, I recommend the Ibex Woolies 2 Crew shirt. The Merino wool is soft against your skin and flexible enough to be comfortable for a day spent at your desk or in meetings, but also adventure-ready thanks to its natural thermoregulating and moisture-wicking properties.
Thanks to the sleeves’ thumbhole, you’ve got extra warmth for your hands even if you’re wearing gloves.
The Icebreaker Merino 200 Oasis was built to be the ultimate lounging shirt. Soft Merino wool, gusseted underarms, friction-reducing flatlock seams, a drop-tail hem for extra coverage, and a lightweight fabric that naturally controls moisture, odors, and prevents overheating. Light but wonderfully warm, you’ll love wearing it all weekend long with your cozy lounge pants.
Get heavy-duty with the Carhartt Force. The midweight thermal layer is built to be work- and sport-friendly, made with a sturdy wool-and-synthetic fabric with odor-controlling, moisture-wicking, and high-stretch properties.
The fit, though snug, isn’t so tight it’ll constrict you or slow you down on those days when you need to move fast and work hard. Plus, it’s Carhartt, so you know it’s tough as nails and built to last.