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We ran 23 of the best men's base layers through the wringer to find the warmest, most breathable, and most comfortable options for cold winter days outdoors.
Our team has tested a lot of base layers over the years, and are equipped to offer expert advice to help you find the perfect base layer to add to your kit.
Credit: Justin Simoni
By Justin Simoni ⋅ Review Editor ⋅ Updated April 1, 2026
Whether it's for the warm or cold season, or somewhere in between, a quality base top will help keep you warm, without holding in sweat, so you can stay dry and comfortable, no matter how you like to pace your adventures. Our team has been buying and testing dozens of the best base layers for men on the market for over a decade.
We compare the most popular options side-by-side, scoring them across key performance areas, like warmth, breathability, and drying speed, to hone in on the best thermal tops for your winter and outdoor adventure needs. From the ski slopes to alpine climbs to sleeping out under the stars, our in-depth analysis derives from real-world use testing undertaken while wearing each model.
Our top choice overall is the Smartwool Classic Thermal Merino 1/4 Zip. It's 100% Merino wool, super soft and warm, and has a front zip to help release or retain heat as needed.
If you want wool but need something more affordable, check out the crew-necked Meriwool Merino 250 Long Sleeve, which is around half the price of our favorite Smartwool pick.
If a warm synthetic is what you seek, check out the REI Co-op Midweight Half-Zip. It's comfortable and breathable, features thumb holes, and costs less than most wool options.
Editor's Note: We updated our men's base layer article on April 1, 2026, to include fresh new picks from Mountain Hardwear, Ibex, and Burgeon.
The Smartwool Classic Thermal Merino 1/4 Zip is a winner in the Smartwool lineup, especially when temps drop. Our testers found this layer warm, breathable, and versatile — not to mention incredibly handsome to wear. “Classic” might be in the name, but this base layer includes a few new features built upon the rock-solid legacy of its brethren. A front quarter zip helps dump any excess heat you might have built up while trouncing around a winter wonderland. The top shoulder panel moves the seamlines so they don't chafe when wearing a backpack. “The high collar is one of my favorite features on this top,” our lead reviewer notes. Wool is a near-perfect natural fiber for base layers, and the 100% Merino wool used in the Classic Thermal Merino is among the highest-quality we've tested.
SPECIFICATIONS
Fabric Weight Class
Midweight
Material
100% Merino wool
Fit
Semi-fitted
Odor Control Fabric
Naturally odor resistant
Time to Air Dry
70 min
This top excels in colder temps. “This is THE base layer I grab when conditions get really cold,” Simoni says. “But it will feel like overkill when worn in the heat.” When it's beginning to warm up outside, store this base layer in the closet until the first new flakes start to fall again. A lighterweight layer, like the Smartwool's Classic All-Season Merino, is great when temps are a bit higher. Despite all the amazing characteristics of Merino wool, one of its weaknesses is durability: wearing it around town for an aprés ski drink will be fine, but pit it against anything abrasive, and you'll earn yourself a night watching movies while sewing on patches. Be mindful when washing and drying too, as improper care can cause undue wear to the Classic Thermal, shortening its lifespan. A synthetic top may be a better choice if you're super tough on gear. The Arc'teryx Rho LT Crew is as heavy and warm as a synthetic base layer could get in our lineup and is very durable.
Those looking for the best value for their hard-earned cash should take a serious look at the REI Co-op Midweight Half-Zip, which performs solidly across the board in our tests. The thicker, 220 g/sm fabric retained a good amount of heat while we huffed and puffed up the trail, yet it is also quite breathable, giving your perspiration a chance to leave your skin so you aren't feeling clammy on the descent. The fabric is both soft and durable - a trick many of the wool-based layers have a hard time pulling off. For a more price-conscious base layer, it still packs a ton of well-thought-out features, from its stealth thumb loops and half-zipper to its high, padded collar. Flatlock seams throughout round out this well-designed base layer. “Its warmth, coupled with the impressive durability we saw after repeated use, is a winning combination in harsh conditions,” notes our lead reviewer.
SPECIFICATIONS
Fabric Weight Class
Midweight
Material
92% recycled polyester, 8% spandex
Fit
Semi-fitted
Odor Control Fabric
None
Time to Air Dry
55 min
Being a jack of all trades, you're not going to find the REI Co-op Midweight Half-Zip a master of any one standout role. We've tested much warmer base layers and more feature-rich options. If you'd rather have the benefits of wool, the Icebreaker Merino 200 Oasis Half Zip is another partial zip option that scores on par with the REI model. It is just as comfortable and slightly warmer and lighter, but also slightly less durable. The Arc'teryx Rho LT Crew may be an even warmer synthetic base layer, but it lacks the half zip and thumb loops. For the price, the REI Co-op Midweight Half-Zip pulls off the very difficult trick of working really well in a wide variety of conditions, adding even more value to this top.
Thumb loops like the ones found on the REI Co-op Midweight Half-Zip help both to keep your hands warm and prevent the sleeves from getting lost under a few other outer layers. It's one of our favorite features. Credit: Justin Simoni
For the coldest of winter days, we're thankful for heavy base layers, but most of the time, we're better off with a top that's still warm but much more breathable. For us wool-lovers, the Ibex Woolies Pro Tech Crew answers the call for a stretchy, comfortable, and warm enough base layer we can put on when cold fronts roll through. Its wool/synthetic Nuyarn fibers work together, allowing each to express its strengths: the wool filaments loft up for excellent heat-trapping performance, while the nylon core adds strength and stretch. Both work in unity to enhance loft and wicking abilities. “The Ibex Woolies Pro Tech Crew slim fit and generous stretch provides a wonderful next-to-skin feeling, that seems to really move sweat away from my body, keeping me feeling comfortable”, says our tester.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Material
85% Merino Wool, 15% Nylon
Fit
Slim fit
Odor Control Fabric
Naturally odor resistant
Time to Air Dry
25 min
In fact, the Ibex Woolies Pro Tech Crew is one of the lightest base layers in our lineup, competing with full-on synthetics for the crown. It's lightweight construction is one of the reasons why it's so breathable and performant, but it comes with the compromise of not being as durable as thicker layers. “This layer feels so good to wear, but I make sure to wash it gently and always dry it on the line”, attests our tester. “For a base layer this amazing, I'm happy to take care of it”. Price is also a premium, so it's worth considering whether a heavier base layer will work better for your wardrobe. For burlier layers, look into synthetics like the Patagonia Capilene Midweight Crew or Helly Hansen Lifa Stripe Crew. These are both fair weather base layers that add sweat wicking capabilities while retaining some body heat. For something inexpensive, try out the Carhartt Base Force Midweight Crew, which works well as an everyday base layer we wouldn't be afraid to wear most anywhere.
Optimized fabric zones for warmth, breathability, and durability
Synthetic blend enhances breathability and permeability
Generously long sleeves and length
CONS
Seams on shoulder crest and armpits
More expensive than less technical options
A warm base layer can feel stuffy, with tightly knit fabric that doesn't breathe as well, while too breathable base layers may not feel warm enough. The Smartwool Intraknit Thermal Merino tries to solve this conundrum by constructing a shirt with different areas of the fabric that have optimal characteristics for the job they need to perform. For example, the back and armpits are just a little more breathable, the elbows are a little more durable, and extra stretch is found at the ends of the sleeves and on the sides. This all adds up to better performance from a single top, making it perform well under different conditions. “I'm often wearing a backpack, so having a more breathable back is certainly a plus. Having tougher fabric on the elbows also helps my klutziness”, says our tester.
SPECIFICATIONS
Fabric Weight Class
Midweight
Material
53% Merino wool, 45% polyester, 2% elastane
Fit
Slim fit
Odor Control Fabric
Naturally odor resistant
Time to Air Dry
45 min
Cost is certainly a factor to consider when buying the Smartwool Intraknit Thermal Merino, as its price tag is steeper than many alternatives. And for its weight, you won't find it to be the warmest. Seams are very low profile, but the inset sleeves bring two seams together right at the armpits. “My broad shoulders are getting to the limit of what this slimmer-fitting base layer is able to support”, admits our lead tester. Try on the other options available from Smartwool, including the Smartwool Classic All-Season Merino 1/4 Zip for when the weather may be a little warmer, or the Smartwool Classic Thermal Merino 1/4 Zip when temps dip way down.
Our controlled workout tests are a great way to compare base layers in the same environment. We found the Smartwool Intraknit Thermal Merino gets warm pretty quickly, but breaths well, especially for its weight. Credit: Justin Simoni
It may come as a happy surprise that you don't have to empty your wallet for an excellent Merino wool top. The Meriwool Merino 250 Long Sleeve offers near-top-quality performance at a fraction of the cost of most of the 100% Merino base layers we tested. While it lands firmly in the midweight category, our tests prove the extra-fine spun wool that makes up this layer is more breathable than other directly comparable tops, making it a terrific choice for anyone engaged in high-output activities like ski touring. Couple that with a slim, stylish fit, and you get a layer you can take from the mountain straight to après-ski. “At the end of the day, I like to keep things simple. I want gear that works without too much fluff. The Meriwool top accomplishes this objective perfectly,” notes one of our lead reviewers.
SPECIFICATIONS
Fabric Weight Class
Midweight
Material
RWS Merino wool
Fit
Slim fit
Odor Control Fabric
Naturally odor resistant
Time to Air Dry
65 min
While our testers found the Merino wool soft, they also found it a bit itchy initially. “My heart sank a little when I first wore the Meriwool Merino 250 as I felt a little itchy. But after a few wears and a wash, the fabric began to soften and became far less of an issue,” Simoni reports. A design improvement we'd like to see in the future is moving the seams off the top of the shoulder, which we found can rub when wearing a heavy pack. An alternative top with offset seams is the pricier Smartwool Classic Thermal 1/4 Zip. A tradeoff with the low price point of the Merino 250 is durability: the extra-fine fibers are no match for anything abrasive. You'll find a synthetic base layer, like the Under Armour ColdGear Base 4.0 Crew, far more durable. Despite these shortcomings, this top is a reasonable entry point into all-natural base layers for those in the market. It is the perfect companion for cool-weather camping during spring and fall, works well for both resort and backcountry skiing, and is most certainly stylish enough to be worn casually.
For a no-nonsense, simple, comfortable, and fairly durable base layer, grab the Carhartt Base Force Midweight Crew. This is a great top for everyday use, perfect to bring along just in case the weather turns during lunch or a brisk, after-work walk. “I toss the Carhartt Base Force in my pack just in case it gets a little chilly on my bike ride home,” mentions Simoni, our lead reviewer. The polyester waffle knit isn't the warmest, but it's very soft and comfortable, and the loose cut combined with that retro pattern makes for an easy addition to your daily wardrobe. It's built tough enough to be worn as your top layer and isn't so technical that it'll look out of place in casual settings. Plus, you can wash and dry the top with the rest of your everyday clothes. “Because it's so easy to clean — especially compared to my wools — I wear the Base Force Midweight Crew more often,” says Simoni. This base layer is a good value for the performance it lends out.
SPECIFICATIONS
Fabric Weight Class
Midweight
Material
100% polyester
Fit
Loose
Odor Control Fabric
Anti-odor treatment
Time to Air Dry
46 min
Unfortunately, the Carhartt Base Force Midweight doesn't check all the boxes for absolute performance. Our tests show the breathability is excellent, but the trade-off is reduced warmth. The 100% Merino wool Smartwool Classic All-Season Merino 1/4 Zip offers better warmth without compromising too much breathability. To stay with synthetics that don't look out of place as your top layer, the REI Co-op Midweight Half-Zip will be a great choice for more extreme wintry backcountry missions where warmth is key.
Comfort is a big selling point of the Carhartt Base Force Midweight Crew, thanks in big part to the seam patterns that allow a generous fit and move the seams from trouble areas, like the top of the shoulders. Credit: Justin Simoni
For next-level breathability as well as impressive warmth from a synthetic base layer, try on the Burgeon Alpha Direct 90 Hoodie. The use of the extremely technical Alpha Direct fleece sets this top apart from most everything else in our lineup. Not only is this fabric super lightweight, but it also holds on to very little moisture when it does get wet, leading to unbelievably fast on-the-line dry times. “The Burgeon Alpha Direct 90 Hoodie is a great choice for anytime you need warmth but don't want to be weighed down by heavier options,” notes our lead tester, who's also a fanatical ultralight backpacker.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Material
100% Polyester
Fit
Loose
Odor Control Fabric
None
Time to Air Dry
23 min
The Alpha Direct fabric used on the Burgeon Alpha Direct 90 Hoodie seems flawless, but it has one major weakness: durability. The exposed fleece fibers that make it so good at retaining warmth can get snagged on anything you brush up against, even on elements of your own clothing, like velcro straps. This is primarily a layer you need to wear underneath something more hardy, like an outer layer, or when you're burrowed deep in a soft sleeping bag. “The fit is also a little non-standard, with a short length, wide waist, and an oversized hood”, notes our tester. Another technical fleece with slightly more durability is the Mountain Hardwear Airmesh, which is also sewn with impressively high-loft, lightweight fleece. For even more durability at the cost of warmth, grab the Patagonia Capilene Midweight Crew. Lastly, the Bergeon is very thin, and while we love the lighter-weight insulation for shoulder season and alpine summers, it doesn't provide the warmth we like to have in deep winter. But if you prioritize weight savings and value breathability, it is a fantastic tech-advanced option.
We love to sing the praises of Merino wool, but the price can be a real-world barrier to owning a quality Merino piece. For those who want to dip their toes into wool, but aren't ready to pony up for the large price tag that can go with it, we wholeheartedly recommend the Merino.tech Crew, a lightweight, 100% Merino wool top knitted with ultra-fine fibers, which gives it a soft, itch-free feel. The tight fit makes it excellent for layering below your mid and outer layers during cold days, or for wearing alone while snuggled into a sleeping bag while camping in brisk conditions. “The lighter fabric weight of the Merino.tech Crew is usually what I prefer on my chillier runs. I tend to build up a lot of heat, so a lighter base layer like this works the best for me,” notes our lead reviewer.
SPECIFICATIONS
Fabric Weight Class
Lightweight
Material
100% Merino wool
Fit
Semi-fitted
Odor Control Fabric
Naturally odor resistant
Time to Air Dry
55 min
With such an incredible price comes some sacrifices. Most notably, the 100% Merino wool will be less durable than many other Merino blend tops we tested, like the Smartwool Intraknit Thermal Merino. Incorporating polyester into wool enhances abrasion resistance. Washing and drying wool also requires care to preserve the material. The Merino.tech Crew utilizes overlock seams instead of flatlock seams throughout, which might irritate those with more sensitive skin. Fit-wise, “It's a little tight underneath the arms for me,” admits our lead reviewer. If that's all a deal breaker, the truer to size Meriwool Merino 250 Long Sleeve is constructed with flatlock seams. It's also much thicker, warmer, and slightly more durable than the Merino.tech Crew.
Seen under a microscope, the Merino.tech Crew shows to have fine 100% merino wool in a tight knit. Credit: Justin Simoni
Product Comparison Table
A warm and comfy base layer is perfect for watching the sunset below snowy peaks. Credit: Justin Simoni
How We Tested
With every review, we identify the key metrics and develop a test plan to carry out in the field. In the case of base layers, we start with only the best tops on the market and then proceed to field-test the heck out of them. Metrics such as warmth and breathability are the heavy hitters, and testing them can be as straightforward as wearing the garments in cold weather (which we do a lot) and noting the relative differences, as well as wearing them indoors in a more controlled setting to compare. Other metrics, like durability, call for a combination of field use (i.e., chimney climbing and bushwhacking) and lab testing (repeated dry and wash cycles and an abrasion test). From the high desert of the US Southwest to the craggy peaks of the Pacific Northwest, we wore these tops through a variety of activities — mountain biking, climbing, uphill and downhill skiing, trail running, backpacking, and more — evaluating their relative strengths and weaknesses along the way.
Our base layers testing is divided among six rating metrics:
Warmth (25% of total score weighting)
Breathability (20% weighting)
Comfort and Fit (20% weighting)
Durability (15% weighting)
Drying Speed (10% weighting)
Layering Ability (10% weighting)
For more information on our testing process, see our How We Test article. The right layers can make or break a day in the backcountry, and we have the test results to prove it. We've got the scoop on how to nail your layering system, from the warmest fleece jackets and our favorite long underwear bottoms for staying toasty.
We hands-on tested these base layers to ensure we found the best of the best. Credit: Justin Simoni
Why Trust GearLab
Tester and review author Justin Simoni lives for the rarefied air of his backyard mountains in Colorado and keeps his wits sharp with year-round ascents of Longs Peak — usually with a bike-from-town approach. Simoni has been taking part in long-distance bikepacking races and chasing mountain FKTs for over a decade, including the Tour Divide, Colorado Trail Race, and his own self-powered 14er challenges. If there's one thing he knows, it's being on the right side of chilled on some desolate ridgeline at 13,000', waiting for the warmth of the rising sun and wearing a big grin while he sleeps.
Our expert for all things comfortable and cozy is Aaron Rice. Growing up on the Atlantic coastline and living up and down the Rocky Mountains for more than a decade, he knows all about making the most out of cold-weather playtime. A passion for winter weather led him to a bachelor's degree in snow and climate science. As a ski patroller and avalanche educator, you can often find him huddled in a snow pit, happily freezing his butt off to discuss the finer details of stellar dendrites. Together, these two make a base-layer dream team.
From deserts to the peaks and everywhere in between, our team took these base layers on many outdoor trips to figure out which one is best for your own adventure.
Analysis and Test Results
As a workhorse for thermoregulation, we understand the importance of having the right base layer for your outdoor pursuits. By submitting them to the wear-and-tear of everyday use and a variety of outdoor activities across a spectrum of temperatures and environments, we are best able to dial in which types of layers work best in what situations.
It is important to note that the scores we assign are determined relative to the other products in the review. We purposefully choose to test the best layers on the market, so a low score in our testing does not mean a product is not worth its mettle. It simply means it performed poorly relative to the competition. We understand that your own personal needs will dictate which metrics are most important to you. By testing and rating each layer against one another, we can highlight which products score highest on the metrics that matter most for how you intend to use your base layer.
Worse Value
Better Value
What's the Best Value?
The balance between price and value is a fine line to walk when researching a product, and for base layers, the biggest difference is in the material. In short, synthetics are typically cheaper, while Merino wool options are a bit pricier, but there are budget versions to be found in each category. If you're value-minded but want the benefits of Merino, add a little warmth with an all-natural option like the Meriwool Merino 250, a 100% Merino wool layer that is very reasonably priced compared to its direct competition. It is a standout for 3-season recreation and works quite well as an athletic base for the coldest months. For synthetics, we've been very impressed by the value of the REI Co-op Midweight Half-Zip. It's fairly heavy, at 220 g/sm, which is good enough for wintry excursions, and its price tag will allow you to budget for some après-ski/snowshoe libations.
Along with being made with warm, tough fabric, the REI Midweight Half-Zip has thumb loops and its name sake zipper for a well-rounded layer. Credit: Justin Simoni
The Helly Hansen Lifa Stripe Crew is one of the more affordable base layers we've tested and is a great layer for high-output activities in cold weather, like cross-country skiing. For a casual layer, the Carhartt Base Force Midweight Crew is affordable, though it's less well-suited to sweaty exercise sessions than a comfy top layer for afternoons cruising around town on your bike or taking the dog on a walk.
Early bird gets the worm, or a summit bid all to ourselves in this case. The boys all wore different weights of Merino wool baselayers on this climb up Mt. Hood. Credit: Adam Zagorski
Less, sometimes, is more - if you're looking to go fast-and-light on your next backpack, think about investing in good base layers that can be worn in a wide-range of temperatures, and that allow you to ditch some of your bulkier clothing when the season permits. Credit: Jill Rice
Purposeful Purchasing
One of the best ways we believe to determine value is to start with the following questions:
How do I intend to use this particular layer?
Do I want a layer that will keep me warm during the coldest months of winter?
Or do I want a more versatile layer for the in-between seasons?
These types of questions will help guide you toward what matters most to you as a buyer. Decide which metrics are most important for your sport or activity—whether that's ice climbing or shoveling snow in your driveway—and base your decisions on those factors first.
Warmth
As the foundation of your layering system, warmth is one of the most essential qualities to consider when choosing your base layer. It is not just about simple heat retention but rather the complex system of thermoregulation. A good base layer should trap heat to keep you warm in cold temperatures while also allowing excess heat to escape as your heart rate and body temperature rise. It also involves wicking away sweat to keep you dry and protected from evaporative cooling. All of these ingredients are essential to a layer's ability to keep you warm and dry through a range of temperatures. An intensely warm top that doesn't breathe well may work for ice fishing, but it will likely leave you dangerously wet and cold during high-output activities like backcountry skiing.
We wore these layers through the varying temperatures of Fall, Winter, and Spring to test every quality that helps you stay warm and dry. We wore them as we skinned up windblown ridges in the Northwest, rowed through desolate canyons in the Southwest, slept on the frozen dirt after climbing sunny sandstone cracks, and explored trails by bike and foot in Colorado and New Mexico. The standout tops for well-balanced warmth are the Smartwool tops, the REI Co-op Merino 185 Long-Sleeve Half-Zip, and the Icebreaker Merino 200 Oasis Half Zip. These tops are made from thicker, cushy fabrics that seal in heat while maintaining excellent breathability and moisture-wicking.
Our exercise test helps us understand the warmth and breathability qualities of each base layer. The Smartwool Classic Thermal Merino 1/4 Zip made us work up a sweat in these more controlled, indoor conditions! Credit: Justin Simoni
For the deep cold of winter, we recommend the SmartWool Classic Thermal. It's the heaviest 100% Merino layer we tested, designed specifically for snow sports.
If you want a layer for high-intensity aerobic activities or versatility across seasons, you'll probably benefit from a lighter-weight, more breathable option. We were extremely surprised by the performance of the lightest-weight options, which are made of very technical fleece without a face or backing fabric and, at first blush, don't seem like they'd be super warm. The Burgeon Alpha Direct 90 Hoodie is best worn under a more wind-resistant layer, but bumps up the warmth of any layering system you add it to more than its paltry weight would have you even believe.
The Burgeon Alpha Direct 90 Hoodie acts like an undercoat supercharging your top layers in locking in warm air but giving up perspiration easily. Credit: Justin Simoni
For cross-country and backcountry skiing, we would choose lightweight layers that still offer a little warmth, like the Outdoor Research Alpine Onset Merino 150 Crew or the Helly Hansen Lifa Stripe Crew. If you're a rock climber anticipating long belay stances and short bursts of energy, check out the Icebreaker Merino 200 Oasis Half Zip, which provides a solid level of warmth but still offers impressive breathability.
The droptail on the Smartwool Intraknit Thermal Merino helps keep your lower back covered even when you're bending down. Credit: Justin Simoni
Some specific features enhance warmth and may help narrow your search for the perfect base layer. Tops like the Icebreaker 200 Oasis, Smartwool Intraknit Thermal Merino, and the REI Lightweight Crew have a drop-tail hem. When skiing, we particularly appreciate the ability to keep our shirts tucked in and snow out of our pants. These design features can also help keep your top from riding up and exposing your back and belly when bending over to put on your climbing skins or reaching for that next crimper while climbing. The Ridge Merino Aspect Midweight hoody doesn't feature a drop hem, but both the front and back of this base layer are extra long to make it easy to tuck in.
As well as an extra long hem on the front and back, the Ridge Merino comes with a built-in hood and balaclava. Credit: Justin Simoni
The Argument Against Cotton
There are significant differences in warmth between natural fibers (Merino wool, silk) and synthetic fabrics (polyester, polypropylene), but either can be a good choice. The key here is that they both continue to insulate when wet. Compared to cotton, which can absorb up to 100% of its weight in moisture, leaving you wet, cold, and miserable, and thus potentially quite dangerous in certain backcountry situations.
Breathability
Breathability is the yin to warmth's yang. Alongside warmth, it is arguably the most important quality of an effective base layer. A fabric's moisture-wicking capability primarily determines breathability. Effectively, this is the ability to collect moisture (in the form of sweat) and move that moisture to the outside surface of the fabric, where it can freely evaporate. A quality, breathable layer will help regulate your body temperature through a range of environments, regardless of your energy output.
Breathability should take top priority during active pursuits and stop/start activities like backcountry skiing, backpacking, or rock climbing. A breathable shirt will allow the moist air hovering over your skin to escape through the material without saturating the fabric, thus keeping you warm and dry. Breathability is less important when you are engaged in more passive activities, like riding a chairlift at the resort or ice fishing. But a little is always important. A non-breathable shirt will leave you wearing a sweat-soaked shirt that is wet, heavy, and potentially dangerous in cold conditions.
The Alpha Direct 90 fabric is so light as to be semi-transparent. Credit: Justin Simoni
The Alpha Direct 90 fabric used on the Burgeon Alpha Direct 90 Hoodie is indeed very lightweight and obviously very breathable. Not the toughest of materials, keep it under a more durable layer for the longest life. Credit: Justin Simoni
The Burgeon hoodie fits a bit loose for our preference, but this also helps with airflow. Credit: Justin Simoni
We assess each layer's breathability with months of hiking, running, skiing, climbing, and biking. We test each layer side-by-side in temperature-controlled indoor environments as well, using the same short, rigorous exercise routine to work up a sweat. After stopping, we time how long it takes for our skin and the inside of our shirts to dry.
Breathability is a common trait when base layers use lightweight fabrics, like seen here in the Merino.tech Crew. Credit: Justin Simoni
More recently, the battle for excellent breathability AND good warmth retention has “heated” up, with more technical fabrics promising to deliver both seemingly diametric qualities with little compromise. No base layer exemplifies this more than the Burgeon Alpha Direct 90 Hoodie, whose namesake Alpha Direct 90 technical fleece is loftier than other wools or synthetics, trapping warm air while allowing water vapor to pass through easily. The Burgeon Hoodie takes this to the next level, being constructed without even a face fabric for maximum performance.
The Burgeon Alpha Direct 90 Hoodie has a tendency to turn one into a (friendly!) fuzzy monster! Credit: Justin Simoni
Not to be completely outdone, the Mountain Hardwear Airmesh has its own take on performance synthetics, featuring an incredibly airy brushed fleece that functions similarly to Alpha Direct, except that it does have a thin face fabric, which makes it a bit more durable, while also looking far less unconventional.
Soft fleece surrounds the wearer of the Mountain Hardwear Airmesh. Credit: Justin Simoni
When it comes to wool/synthetic blends, the very lightweight Ibex Woolies Pro Tech Crew is also astoundingly breathable. It's secret is in its very lightweight 125 g/sm Nuyarn fabric, being both lighter and loftier than many wool and wool/blend options. And unlike the synthetic options mentioned previously, the Woolies Pro's fabric is stretchy.
Thin and stretchy! The Ibex Woolies Pro Tech Crew is unquestionably an airy base layer. Credit: Justin Simoni
If excellent breathability-to-heat ratings dazzle you but you need something much more durable, try on the Patagonia Capilene Midweight Crew, whose polyester fabric shows good breathability and can take a beating from daily wear, though it won't be the warmest.
Durability of the lighter weight Patagonia, Capilene Midweight Crew is just what you need for climbing and canyoneering. Credit: Justin Simoni
Some other picks in our lineup prove that good breathability in your base layer doesn't need to break the bank. The Thermajohn Long Sleeve Thermal Compression also scores well for breathability, but we didn't find it as warm as its name suggests. The Carhartt Base Force Midweight Crew also scores well for breathability and remains reasonably warm compared to several other lower-cost synthetic options. The Merino.tech Crew — a 100% merino wool base layer — returned exceptional breathability scores care of its very lightweight fabric.
The Access Heavyweight Thermal Crew gives more than reasonable air flow results in our portable meter. Credit: Justin Simoni
Several warmer options made of a Merino blend allow lightweight yet strong fabrics to be spun up into beautifully breathable base layers. These thicker, loftier fabrics are often also airy and easily allow water to pass through them. These include the 150 g/m² Outdoor Research Alpine Onset Merino 150 Crew as well as several base layers that also feature front zippers allowing for enhanced thermoregulation like the 150 g/m² Smartwool Classic All-Season Merino 1/4 Zip and the 185 g/m² REI Co-op Merino 185 Long-Sleeve Half-Zip. These all make excellent options for layering in colder conditions while keeping you relatively dry and fresh.
The REI Co-op Merino 185 Long-Sleeve Half-Zip is an excellent Merino wool blend base layer with a front zip that works well in cool to cold conditions. Credit: Maddock Rigby
Comfort and Fit
If a layer excels in all other categories but fits poorly or is uncomfortable, you probably won't wear it. This may be the toughest metric to rate because comfort and fit are ultimately subjective and depend on personal preference and body type. A few starter questions to ask: How does the fabric feel next to skin? Is it soft, itchy, stretchy, static, warm, or cool? Does it glide against your skin or cling too tightly? Is it loose, tight, or constricting in key areas? Are there gusseted underarms, purposeful stitching patterns, or articulated zones to help freedom of movement? You get the idea.
If you're looking for an athletic-fit base layer without a hood or thumb loops, the REI Co-op Merino 185 Half-Zip is a top choice. The gusseted pits give great freedom in the shoulders, which is especially helpful when you layer up and want to avoid pinch points. The Smartwool Intraknit Thermal Merino is super stretchy all-around, but it also has variable knitting throughout, with some parts of the baselayer being even stretchier, like the sides and ends of the sleeves, to help almost eliminate pinch points.
Several parts of the Smartwool Intraknit Thermal Merino are impressively stretchy.
For stretchy Merino blends, the Smartwool Classic All-Season Merino 1/4 Zip is the king of the hill. It's the lightest Merino top Smartwool makes and has stitching designed to get out of the way of pressure points while carrying a loaded backpack.
If softness can never be secondary, look no further than the 100% Merino Smartwool Classic Thermal Merino ¼ Zip. The high collar keeps your neck warm, and the quarter-zip lets it out of the way when you need some fresh air to circulate. The sleeves are perfectly sized to roll up past the elbows and shoulder panels, and the flatlock seams have been moved away from the crest of your shoulders. The Ortovox 185 Rock'N'Wool Long-Sleeve also earns five stars for its soft, comfortable next-to-skin feel and is a perfect pick if you're looking for something a little lighter.
The Smartwool Classic Thermal Merino 1/4 Zip's high collar rests comfortably on top of one's shoulders when not fully zipped up. Credit: Justin Simoni
If you need something synthetic and cozy, try the Arc'teryx Rho LT Crew, which has a soft, fleece-like inner that feels nice against your skin.
A semi-athletic fit of the Arc'teryx Rho LT Crew fits well underneath other layers, without feeling constrictive. Credit: Justin Simoni
Durability
We often spend more on fewer, high-quality products in hopes that what we own will both last us longer and stay out of the landfill. Base layers should adhere to the same purchasing ethics we apply to all our consumption habits: buy less, buy quality, and repair when possible. When that's not possible, opt for post-consumer products — many of the polyester layers included in this review are at least partially made from recycled fibers.
To test durability, we assess the strength of the fabrics, the quality of the stitching, and the overall construction of the pieces. We also drag them up against rocks, roll them in the dirt, bushwhack through manzanita and chaparral to get to beautiful places, and subject them to merciless cycles of washing and drying. To test abrasion resistance in a controlled environment, we grind the fabric a set number of times across a one-foot distance of gritty sandstone to see how it fares (think washboard technique). This specific test gives us a clear idea of how certain tops will withstand long-term abrasion.
Making its way up an Eldo classic, the Smartwool Classic shows off its ability to breathe and keep you comfortable in warm conditions as well as cold. The thick Merino fabric makes it among the most durable Merino layers that we tested. Credit: Roland Mott
Unsurprisingly, base layers made of thick synthetic fabrics are the most durable. In contrast, 100% Merino wool base layers — no matter their thickness — tend to test as the least durable. Some base layers are made with Merino wool blended with polyester, nylon, and/or elastane. The higher the percentage of other materials blended in, the more durable the fabric becomes. However, the durability never matches that of pure synthetic. Thin fabrics, regardless of composition, perform worse in our durability tests.
We love the lighteight of the Ibex Woolies Pro Tech Crew but even with synthetic blended into the wool, it's a more delicate layer than many pure synthetics that feature a much a tighter knit. Credit: Justin Simoni
The Under Armour ColdGear Base 4.0 — a thick synthetic — was our absolute standout, seemingly unaffected by our harsh abrasion test. It would be a good choice for those who are doing heavy work outside. Almost as tough and just as warm is the REI Midweight Half-Zip. It features fabric with a slightly softer hand, and we found it quite comfy for all-day treks and all-day movie-watching sessions.
The Access Heavyweight Thermal Crew is a great choice for landscaping and yard work. Credit: Justin Simoni
For how thin it is, the synthetic Patagonia Capilene Midweight Crew also scored well for durability. It would work well as a top layer for warmer days. The Helly Hansen Lifa Stripe Crew held up almost as well and would fit well for a variety of outdoor activities, be it hitting the slopes, going on a snowshoe, or exploring some slot canyons. When choosing Merino, stick with the blends if durability is tantamount.
Durability for the thickness of its fabric is excellent on the Patagonia Capilene Midweight Crew and the minimal stitching means less seams in the way of other gear like our backpack. Credit: Justin Simoni
The Smartwool Classic All-Season also scored among the most durable blended tops we tested and should suffice for most activities when worn under a more durable layer and washed properly.
For cold conditions outside, the Under Armour ColdGear Base 4.0 works well and can take much more work abuse than other comparably warm wool base layers. Credit: Maddock Rigby
Merino Care
Although the care instructions on some Merino wool garments allow tumble drying on low, we suggest washing on a cold cycle and laying flat to dry. This will increase the longevity and fit of your shirt. This fabric also holds an uncanny power to resist body odor, whereas synthetic fabrics are infamous for holding onto and sometimes even enhancing stink. This means that wool can be worn more and washed less, increasing its longevity.
Drying Speed
Sometimes, moisture comes from outside sources, such as rain or snow. Other times, it comes from working hard and pushing yourself — aka sweat. No matter where it comes from, a top's ability to dry quickly on the body is important.
The drying speed of a fabric can differ depending on whether it is being worn or hung out to dry. In our experience, there is a strong correlation between drying speed and breathability — that is, tops that dry faster on the clothesline also tend to dry faster on our bodies. When dealing with dry times, you may also want to cross-reference them with warmth, as lightning-quick dry times of thinner base layers may also mean a less warm base layer.
Thinner base layers like the Ridge Merino Aspect Midweight Merino Balaclava Hood have a greater chance of drying fully faster, which could be important to you if you're waiting for something to dry while finishing up a meal. Credit: Justin Simoni
Our drying speed test is simple. We run all our base layers on a wash cycle, then hang them out and time how long it takes for them to dry completely. We give bonus points to thicker base layers that we find have dried at the same time as thinner ones. Thinner fabrics dry faster than thicker ones, and loftier fabrics dry faster than denser weaves.
Colorful and practical, our soak n' dry test seeks to replicate how you would hand wash and air dry shirts while on an expedition or extended backcountry trip. Credit: Aaron Rice
The technical fleece found on the Burgeon Alpha Direct 90 Hoodie and Mountain Hardwear Airmesh are two tops that are thin, lofty, and lightweight, all three attributes that help them dry faster than almost anything else in our lineup.
The Burgeon Alpha Direct 90 Hoodie resists getting saturated with water and we found it dries fast enough to be ready after a short nap on backpacking trips. Credit: Justin Simoni
One surprising result came from the Ibex Woolies Pro Tech Crew, a wool/synthetic blend. It's a very lightweight top with impressive loft for its 125 g/sm weight and incredible on-the-line dry times, making it perfect for those looking for a fast-drying wool option. Merino wool claims to absorb up to 30% of its weight in moisture before feeling wet to the touch. This seems reasonable, as we have to agitate and compress the wool layers while submerged for the fibers to become saturated — a plus if you are planning to wear wool layers alone in wetter, milder climates.
The Ibex Woolies Pro Tech Crew will dry fast when left outside in the sun. Credit: Justin Simoni
The synthetic Patagonia Capilene Midweight Crew and Thermajohn Long Sleeve Thermal Compression were not far behind in drying speed. The polyester Carhartt Base Force Midweight Crew impressed us with its drying speed, adding to its appeal as a casual grab-and-go layer for everyday outings.
A surprising finding in our dry test was the Under Armour ColdGear Base 4.0, the thickest synthetic we tested. Despite its thickness, it dried more like a thinner, midweight layer. Notably, the Merino wool Ortovox 185 Rock'N'Wool Long-Sleeve and Meriwool Merino 250 dry quicker than other 100% wool layers of similar weight.
Consider when and how you plan to use your base layer. Choosing a layer that balances active drying and warmth is crucial for sports like backcountry skiing. Credit: Aaron Rice
Layering Ability
Base layers are meant to be worn next to the skin and paired with heavier over layers, but we love a versatile base layer that can be worn as a standalone top or layered in myriad ways to keep you warm and comfortable in any temperature or situation.
To test the layering ability, we consider all ways a top can be layered and try all combinations with each piece. We note how easily they layer as well as how they fit and feel: next to skin, over a t-shirt, over another base layer, under a sticky and tight fleece mid-layer, a sweatshirt, a puffy, a rain shell, as well as stacked in a full layering system of first (base) layer, mid-layer, puffy, and hard shell. While all of the tops in our review perform well next to skin, a few work great layered in other ways, too.
An example of a layering system, where a light, tight-fitting base layer is put on first, then the looser and thicker Smartwool Classic Thermal Merino 1/4 Zip is worn on top, with a heavy insulated down jacket as the outer layer. Credit: Justin Simoni
We were also impressed by the layering of the REI Co-op Midweight Half-Zip, which has a high collar and a front zip to help keep warm and dump excess heat quickly. The front-facing fabric is smooth and won't catch on any upper layers.
Another example of a layering system: we used the REI Co-op Midweight Half-Zip as our base layer, with a gridded fleece mid layer over that, and a down puffy jacket over everything. Credit: Justin Simoni
Another standout for its layering ability is the Ridge Merino Aspect. Its balaclava hood provides coverage and stores away easily, keeping your other layers out of the way. Thumb loops anchor the extra-long sleeves, so this layer won't disappear up your sleeve when you put on an additional mid or outer layer.
The Aspect Midweight Merino's balaclava hood works well alone, or with an outer layer. Credit: Justin Simoni
For a warmer option, the Smartwool Classic Thermal Merino is both handsome and functional. The quarter-zip and cuffs, which are loose enough to roll up, help regulate temperature. Its casual fit means there's room for another thin base layer underneath for added warmth on the coldest days. The Smartwool Intraknit Thermal lacks a front zipper, but the Merino blend lofts well, keeping it warm yet light on its own, or it can be easily layered with something else.
The midweight Intraknit layers well with other performance-type outer layers and is heavy enough to be used as a mid-layer itself. Credit: Drew Crittenden
How to Choose a Men's Base Layer
Base Layers play an important role in keeping you comfortable while you enjoy your outdoor passions. Since they're next to your skin, they're what you'll feel when you're hiking a long trail, enjoying a brisk morning bike ride, or traversing over a mountain range on skis.
Your base layer is the anchor for the rest of your upper body layering system. Credit: Justin Simoni
What's the Difference Between the Types of Fabric?
Natural and synthetics, cotton/wool/polyester — blends! All the different types of fabric can get confusing! The synthetic vs. all-natural fibers argument is a perpetual battle in the world of recreational apparel, and we'd like to think of ourselves as conscientious objectors. There are certainly pros and cons to each material type, and the ultimate goal is to choose fabric that keeps you warm, is breathable, wicks moisture, and is durable enough to last a long time in your gear closet.
Wool
Wool is one of the most popular choices. Merino wool tops are typically more expensive, but they offer benefits such as superior body temperature regulation, moisture-wicking, and odor resistance. Most of the warmest base layers we highlight are made of wool, as it has a natural loft that traps warm air and prevents it from escaping while also having impressive wicking abilities. And even when wool does get wet, it retains much of its warmth, meaning you won't start shivering once you build up a sweat. Wool can be finely spun to be incredibly soft and comfortable next to your skin.
The downside of merino wool is its notorious lack of durability. You'll have to be a little more careful with wool when you're wearing it as a top layer and when laundering. It tends to snag, wear through quickly, and/or shrink and lose its shape after repeated washings. But for many folks, the performance benefits of Merino wool outweigh its lack of durability, and with proper care, your Merino top can serve you for a long time. Despite its reputation as a relatively short-lived fabric, several of our testers have gotten many years of use out of theirs. That said, they try to hang them up to dry and not wear them every single day (they are certainly comfortable enough to want to do just that in the winter).
A 100% wool base layer offers some of the best performance in warmth. Credit: Justin Simoni
Wool Blends
To counter the fragility of 100% wool, manufacturers often weave synthetic fibers with wool for a more durable material that's resistant to abrasion and stretching, all while minimally impacting the warmth and softness of the wool itself. They add desirable characteristics like durability and stretch, and can enable thinner fabrics, but they're almost always more expensive than 100% wool. The tech here is getting better and better as manufacturers find new ways to weave, layer, and blend the two materials together, and some of our most-worn tops are blends, many of which are still going strong after years of use.
The Smartwool Intraknit Thermal Merino is wool/synthetic blend with polyester fibers that adds strength and a little more durability as well as elastane to add a ton of stretch. It's a little more durable than straight 100% merino wool, but won't take the level of abuse of some pure synthetics. Credit: Justin Simoni
Synthetics
Synthetic fabrics tend to be less expensive, a touch more durable, and pack down smaller. They also tend to retain odors over time, and often don't offer the same warmth-to-weight ratio as their natural-fiber counterparts. But they can be much quicker drying and more breathable than wool, depending on how the fabric was manufactured.
Polyester base layers come in a variety of styles and weights. This top is a mid-weight, which works across many different temperature conditions except the very warm or the very cold. Credit: Justin Simoni
One of the newer, more intriguing synthetic fabrics is super-technical fleece, which also eschews backing and even face fabric to maximize the amount of warm-air-trapping insulation for its weight while increasing breathability. They're surprisingly warm, but also even more delicate than 100% merino wool. Nevertheless, they are a great choice as an active insulation layer and for warmer weather duties.
The Mountain Hardwear Airmesh only has a thin face fabric holding onto technical fleece that traps a ton of warmth in its fibers. Its' even designed to be reversible, where the fleece can be more effective albeit at a cost of putting the most delicate part of the top on the topside. Credit: Justin Simoni
What Seasons Are You Shopping For?
Base layers are meant to add a boost of warmth as the foundation for your layering system and can be worn year-round for different activities, but how much warmth you need will depend on where and when you spend the most time outside. If you like to hang out on chairlifts and aprés ski bonfires in the dead of winter, consider a heavier-weight base layer that will retain more heat, even when your body is at rest. If you're planning to be actively moving rather than just standing still, warmth will come second to breathability. The base layer that works great for skiing won't be best for backpacking in August, and you'll want to go with a much lighter, thinner layer for active days. If you want a good all-rounder that you can layer up in the winter, wear alone in the summer, or under a light jacket in shoulder seasons, a mid-weight layer will be your most versatile option.
One usually benefits from wearing a heavier and thus warmer base layer during colder conditions. Credit: Justin Simoni
Wool layers are usually sold with the weight specified in grams per square meter (g/sm), while synthetics are usually just labeled as lightweight, midweight, and heavyweight. This can be a helpful first step in estimating the warmth and breathability of a shirt, but the fabric's weave has a significant impact here as well.
Conclusion
With such a wide array of options out there, it can be tough to narrow your search down to the layer that best suits your body type, internal temperature inclination, and intended uses. We conduct all of our tests and summarize our experiences to try and help you choose the layer that will become your adventure sidekick for years to come. You need to consider activities, temperature ranges, features, and qualities when choosing a new base layer top. We wish you luck in your honorable pursuit of having fun outside.
