Reviews You Can Rely On

The 5 Best Base Layers of 2022

We tested men's base layers from Smartwool, Patagonia, Cotopaxi, Black Diamond, and more to find the warmest and most comfortable options
Best Base Layer of 2022
The front 1/4 zip on the Smartwool Classic Thermal Merino helps with dumping excess heat quickly, coming in handy when you're layered up and conditions change quickly.
Credit: Justin Simoni
Saturday November 12, 2022
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For a decade, our team of experts has bought and tested dozens of the best base layers on the market. For this update, we compare 18 of the most popular options side-by-side. From the ski slopes to alpine climbs to sleeping out under the stars, our in-depth analysis derives from real-world adventures undertaken while wearing each model. We score all base layers across key areas of performance, like warmth, breathability, and drying speed. Whether it's for the warm or cold season, a quality base layer is sure to keep you dry and comfortable, no matter where your next outdoor escapade takes you.

Because we know men's and women's versions of the same products don't always perform identically, we had our team of female testers assess the best women's base layers. We know the right layers can make or break a day in the backcountry. Luckily, we've got the scoop on how to nail your layering system, from comfortable underwear to protective outerwear. We've also selected our favorite long underwear bottoms and the best and warmest fleece jackets to keep you toasty.

Editor's Note: This review was updated on November 12, 2022, after reassessing our full lineup and bringing on 9 new products.

Related: Best Base Layers for Women

Top 18 Product Ratings

Displaying 1 - 5 of 18
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Awards   Best Buy Award  Editors' Choice Award 
Price $100 List
$70.00 at Amazon
$35.95 at Amazon$65 List$90 List
Check Price at REI
$115.00 at Backcountry
Compare at 2 sellers
Overall Score
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80
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Pros Tough and thick fabric, fast drying for the weightExtremely breathable, lightweight, dries fast, super affordableSoft and stretchy fabric gives freedom of movement, great value, thumb loopsThin and lightweight Merino blend, 1/4 zip enhances thermal regulation, extra long sleeves and torsoSupremely warm, exceptionally comfortable, front zip, shoulder panels keep things comfortable with a heavy pack
Cons Thick fabric with slim fit leads to pinch points, sleeves not long enough for thumb loops, many seams stick outPoor fit, not very warm, not super durable, stinkyNot as warm as wool layers of the same weight, risk of smelling if left unwashed after useSlim athletic fit may not work for all body types, thin fabric less durable than other optionsMore delicate than others, pricey, wool may lose shape and sag without proper care
Bottom Line A thick synthetic base layer good for dirty outside jobs from chopping wood to building housesThis top is an impressively breathable and lightweight base layer built for activities where you are creating a lot of heatOne of our favorite super stretchy, soft, and warm synthetic base layers for cool to cold conditionsThis baselayer is sensationally lightweight for a wool blend and notably breathable because of itAn uber comfortable, warm, and breathable 100% Merino wool base layer for the coldest of conditions
Rating Categories Under Armour ColdGe... Helly Hansen Lifa S... Cotopaxi Liso Top Smartwool Classic A... Smartwool Classic T...
Warmth (25%)
7.0
5.0
6.0
8.0
9.0
Breathability (20%)
6.0
8.0
7.0
7.0
7.0
Comfort and Fit (20%)
7.0
7.0
9.0
8.0
9.0
Durability (15%) Sort Icon
10.0
9.0
8.0
8.0
7.0
Drying Speed (10%)
9.0
8.0
9.0
8.0
6.0
Layering Ability (10%)
6.0
6.0
8.0
7.0
9.0
Specs Under Armour ColdGe... Helly Hansen Lifa S... Cotopaxi Liso Top Smartwool Classic A... Smartwool Classic T...
Material 78% polyester, 22% elasterell 100% Lifa Dry 84% recycled polyester, 16% spandex 87% Merino wool, 13% nylon 100% Merino wool
Fabric Weight 40 min 125 g/m² 200 g/m² 150 g/m² 250 g/m²
Weight (size large) 10.6 oz 5.2 oz 8.5 oz 7.6 oz 11.3 oz
Available Cuts Crew, 1/4 zip Crew Crew Crew, 1/4 Zip Crew, 1/4 zip, hoodie
Thumb Loops? Yes No Yes No No
Air Dry Test 40 min 45 min 40 min 45 min 70 min
Fit Slim fit Slim fit Semi-fitted Slim fit Semi-fitted
Stitching Various Flatlock seams Flatlock seams Flatlock seams Flatlock seams
Dryer Safe? Yes Yes Yes Not stated Yes
Shoulder Top Seams? No Yes No Yes No
Drop Tail Hem? No No No No No


Best Overall Base Layer


Smartwool Classic Thermal Merino 1/4 Zip


80
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 9.0
  • Durability 7.0
  • Drying Speed 6.0
  • Layering Ability 9.0
Material: 100% Merino wool | Weight: 11.3 ounces
REASONS TO BUY
Amazing warmth for its weight
Super soft fabric
Front zip helps with heat regulation
Breathable and pleasant to wear even when wet
REASONS TO AVOID
100% Merino wool is delicate
Price tag may turn off thriftier buyers
Special care needed for washing and drying

Smartwool comes out with another winner, especially in colder temps, with the Smartwool Classic Thermal Merino 1/4 Zip. We found this layer warm, breathable, and versatile — not to mention extremely handsome to wear. "Classic" may be in the name, but this base layer comes with a few new features built upon the rock-solid legacy of its brethren. A front quarter zip helps dump any excess heat you may have built up trouncing around a winter wonderland. The top shoulder panel helpfully moves the top seam that would be on the crest of your shoulders down and out of the way from heavy pack straps that can cause discomfort. Wool is an almost perfect natural fiber to use for base layers, and the 100% Merino wool utilized in the Classic Thermal Merino is some of the highest quality we've reviewed.

Since this top excels in colder conditions, it will feel a little overkill when worn in the heat. When it's beginning to look a lot like summer outside, store this base layer in the closet until the first new flakes start to fall again, and pick out a more appropriate base layer to be comfortable in instead. 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.

Read more: Smartwool Classic Thermal Merino 1/4 Zip review

best overall base layer
The Smartwool Classic Thermal Merino 1/4 Zip is great as a base layer to wear while camping as the 100% Merino wool is highly breathable, keeping you both warm and dry while nestled in your sleeping bag.
Credit: Justin Simoni

A High Value Synthetic


Cotopaxi Liso Top


76
OVERALL
SCORE
  • Warmth 6.0
  • Breathability 7.0
  • Comfort and Fit 9.0
  • Durability 8.0
  • Drying Speed 9.0
  • Layering Ability 8.0
Material: 84% recycled polyester, 16% spandex | Weight: 8.5 ounces
REASONS TO BUY
Stretchy
Comfy
Quick drying
Thumb loops
REASONS TO AVOID
Odors develop despite odor control
Lower warmth-to-weight ratio than wool

Infinitely stretchy and stylish, the Cotopaxi Liso Top earns top marks from us in almost everything except absolute warmth. The handsome cut and smooth fabric of the Liso performs excellently as a base layer, allowing you to move freely underneath the shirt and layer up with whatever kit you'll need throughout the day to stay warm, dry, and comfortable. We especially love the addition of thumb loops that keep the extra long raglan sleeves from riding up while we're riding down slopes at Mach 4. Once you're back in the lodge, strip down to just the Liso Top while sipping on hot chocolate and still be confident that this base layer makes you look good all on its own.

If you're ultimately looking for the warmest base layer out there, the Cotopaxi Liso won't fulfill all your needs, as it is thinner and not as warm as others out there. It's also less warm at the same weight than its wool counterparts. The synthetic fabric will develop a funk if you haven't washed it after a few days of use, despite the Polygiene application applied to the fabric. Be mindful when washing the Liso: all that stretch is accomplished by using a hefty amount of spandex in the fabric, and this will lose its stretchiness after enduring too many dryer cycles.

Read more: Cotopaxi Liso Top review

base layer - a high value synthetic
The Cotopaxi Liso's super stretchy synthetic fabric gives you absolute freedom of movement underneath all your top layers.
Credit: Justin Simoni

Best Wool Bang for the Buck


Meriwool Merino 250 Long Sleeve


73
OVERALL
SCORE
  • Warmth 9.0
  • Breathability 7.0
  • Comfort and Fit 7.0
  • Durability 5.0
  • Drying Speed 9.0
  • Layering Ability 6.0
Material: 100% Merino wool | Weight: 10.1 oz
REASONS TO BUY
Affordable
Balances warmth and breathability
Stylish
REASONS TO AVOID
Slightly itchy
Durability left wanting

You may be surprised to discover that you actually don't have to pay an arm and a leg for a superb 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 tops we tested. Even though it is firmly in the midweight category, the extra-fine spun wool used to create this layer is more breathable than other directly comparable models, making it a great option for folks engaged in high-output activities like ski touring. Couple that with a slim, stylish fit, and you have a layer you can take from the mountain straight to après-ski.

Though soft, the Merino wool is slightly itchy at first and takes some breaking in (read: responsible washing and drying) before it is snuggly-comfy. We hope that a future design of this shirt moves the seams off the shoulder top, which can rub when wearing a heavy pack. One thing you do lose with the price of the Merino 250 is durability: the extra-fine fibers are no match for anything abrasive, so keep this base layer away from your rock climbing and canyoneering trips. Beyond these small critiques, this layer presents a reasonable entry point into all-natural base layers. It is the perfect companion for cool-weather camping during the shoulder seasons, works well for both resort and backcountry skiing, and is certainly stylish enough to be worn casually.

Read more: Meriwool Merino 250 Long Sleeve review

base layer - best wool bang for the buck
Coffee warms from the inside, this layer effectively helps keep us warm from the outside.
Credit: Jill Rice

Most Versatile


Black Diamond Solution 150 Merino Half Zip Hoody


77
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 7.0
  • Comfort and Fit 9.0
  • Durability 6.0
  • Drying Speed 8.0
  • Layering Ability 10.0
Material: 78% Merino wool, 22% polyester | Weight: 8 ounces
REASONS TO BUY
Hood, 1/2 zip, and thumb loops
Soft, thin Merino wool blend layers up well
Looks and functions well on its own
REASONS TO AVOID
Slim, athletic fit won't work for everyone
Compromised durability
Pricey

Of all the base layers we have at our disposal, the Black Diamond Solution 150 Merino Half Zip Hoody is the one we've been reaching for no matter the day's objective. The story of the Solution 150 starts out as a solid 150 g/m² Merino wool blend base layer that hits a sweet spot between light and medium base layers, then builds upon that foundation with a helmet-compatible hood, 1/2 zip, and extra long sleeves with thumb loops — all of which help you cover up or expose some skin depending on the conditions you face. The slim, athletic fit works well as a first layer in colder conditions. But it also works well by itself when the temps start to rise, or the after-climbing beers start to be passed around.

The Solution 150 won't be a perfect fit for everyone: the slim fit can be too tight for many body types to wear comfortably — especially if you're worried about the sleeves being too tight around the shoulders and pits. The NuYarn wool blend does a great job of producing a thin, stretchy fabric, but durability is a concern if worn alone and not safely underneath a top layer. Finally, we need to talk about the price: this is one of the most expensive base layers we've reviewed. Still, if you can swing the cost of entry, you may never find yourself not wearing this hoody, from when the first flakes fall to when the last ski run closes.

Read more: Black Diamond Solution 150 Merino Half Zip Hoody review

base layer - most versatile
The Black Diamond Solution 150 Merino Half Zip Hoody makes an excellent do-it-all backpacking top, especially for colder conditions in lieu of a sun shirt.
Credit: Justin Simoni

Best Midweight Layer


Smartwool Intraknit Thermal Merino


77
OVERALL
SCORE
  • Warmth 8.0
  • Breathability 7.0
  • Comfort and Fit 8.0
  • Durability 7.0
  • Drying Speed 8.0
  • Layering Ability 8.0
Material: 53% Merino wool, 45% polyester, 2% elastane | Weight: 8 ounces
REASONS TO BUY
Slim, athletic fit with surprising freedom of movement
Great warmth-to-weight ratio
Durable Merino wool blend throughout with additional protection in elbows
REASONS TO AVOID
Seams found in the usual problem areas
Expensive

The Smartwool Intraknit Thermal Merino wins top honors for its weight class thanks to its innovative seamless knitting technology that blends swaths of warm fabric with panels that add durability and ventilation — all without requiring additional seams, which saves on weight and bulk. We think this is a pretty cool innovation, and it seems to work. The slim, athletic fit excels as a base layer, allowing you to top it off with additional layers for a complete system to prepare you for the harshest of conditions. Extra long sleeves, torso, and a drop tail hem ensure that the Intraknit Thermal covers you no matter how you move. The midweight Merino wool blend fabric is a great "just right" weight to use for most cool to cold days outdoors.

The Intraknit Thermal isn't without its weaknesses. We've noticed more piling of the Merino wool blend than we'd like to see on a base layer priced as high as this one. The higher price point alone, when compared to other base layers, may be enough to dissuade you from purchasing this one. Also, the slim fit may be too tight for comfort, especially around the shoulders, where pinch points can develop when additional layers are worn. We're a little surprised that the Intraknit tech doesn't extend to the shoulders, where instead there are some not-awesome seams. These can rub and cause chafing where pack straps come in contact. Despite these flaws, it's no question to us just how warm, comfortable, and lofty the Intraknit Thermal Merino really is out in the elements.

Read more: Smartwool Intraknit Thermal Merino review

base layer - the smartwool intraknit thermal merino is perfect for keeping alpine...
The Smartwool Intraknit Thermal Merino is perfect for keeping alpine start chills at bay.
Credit: Drew Crittenden

Compare Products

select up to 5 products to compare
Score Product Price
80
Smartwool Classic Thermal Merino 1/4 Zip
smartwool classic thermal merino 1/4 zip base layer review
$115
Editors' Choice Award
77
Smartwool Classic All-Season Merino 1/4 Zip
smartwool classic all-season merino 1/4 zip base layer
$90
77
Smartwool Intraknit Thermal Merino
smartwool intraknit thermal merino base layer review
$125
Top Pick Award
77
Black Diamond Solution 150 Merino Half Zip Hoody
black diamond solution 150 merino half zip hoody base layer review
$145
Top Pick Award
76
Cotopaxi Liso Top
cotopaxi liso top base layer review
$65
Best Buy Award
75
Icebreaker Merino 200 Oasis Half Zip
icebreaker merino 200 oasis half zip base layer
$115
74
Under Armour ColdGear Base 4.0 Crew
under armour coldgear base 4.0 crew base layer
$100
74
Patagonia Capilene Air Crew
patagonia capilene air crew base layer
$139
73
Meriwool Merino 250 Long Sleeve
meriwool merino 250 long sleeve base layer review
$60
Best Buy Award
73
REI Co-op Merino 185 Long-Sleeve Half-Zip
rei co-op merino 185 long-sleeve half-zip base layer
$90
72
Patagonia Capilene Cool Lightweight L/S
patagonia capilene cool lightweight l/s base layer
$55
71
Outdoor Research Alpine Onset
outdoor research alpine onset base layer
$89
70
Helly Hansen Lifa Stripe Crew
helly hansen lifa stripe crew base layer
$45
70
Ortovox 185 Rock'N'Wool Long-Sleeve
ortovox 185 rock'n'wool long-sleeve base layer
$110
68
Odlo Performance Wool Warm
odlo performance wool warm base layer
$100
67
Outdoor Research Echo Long Sleeve
outdoor research echo long sleeve base layer
$52
66
REI Co-op Lightweight Crew
rei co-op lightweight crew base layer
$40
63
REI Co-op Silk Crew
rei co-op silk crew base layer
$50

base layer - from the highest mountains, to the deepest canyons, a versatile base...
From the highest mountains, to the deepest canyons, a versatile base layer is key to keeping you dry, comfortable, and on-the-move across the seasons.
Credit: Aaron Rice

Why You Should Trust Us


For this review, we identified the key metrics essential to effectively grading a base layer top. Then we developed appropriate tests to carry out in the field and lab to test each metric individually. For metrics such as warmth, testing is as straightforward as wearing the garments in cold weather and noting the relative differences. 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 — testing and assessing their relative strengths and weaknesses along the way.

Our testing of base layers is divided across 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)

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. 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. Together, these two make a base layer dream team.

Our testers were more than happy to hop in the saddle to test each...
Our testers were more than happy to hop in the saddle to test each top's ability while lapping our favorite mountain bike trails. The Outdoor Research Echo L/S is a great 3-season top for warm-weather activity.
The temperature swings experienced during spring ski mountaineering...
The temperature swings experienced during spring ski mountaineering is the ultimate test of how a base layer is able to balance warmth and breathability. The Black Diamond Solution handles this activity with a clean style befitting an alpinist.
Trail runs were incorporated into our test plans to assess...
Trail runs were incorporated into our test plans to assess breathability and versatility. Though silk offers a higher warmth-to-weight ratio than other fabrics, it is less breathable than other natural fibers.

Analysis and Test Results


As a workhorse for thermoregulation, we understand the importance of having a base layer that will serve you well through all of your outdoor pursuits. That's why we start with only the best tops on the market and then proceed to field test the heck out of them. 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. We target the most important qualities to analyze and test these layers side-by-side according to these metrics. We offer this comprehensive review to help you land on the best base layer for your own needs.

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 that it performed poorly in relation to the competition. We understand that the individual metrics that are important to some folks may not be as important to others. By testing and rating each of these layers relative to one another, we can highlight which products score highest in the metrics that are significant for how you intend to use your base layer.


Value


The balance between price and value is a fine line to walk when researching a product. The synthetic vs. all-natural fibers argument is a perpetual battle in the recreational apparel world, and we'd like to think of ourselves as conscientious objectors. But for the sake of producing quality reviews, we must decide from time to time what materials are the best for certain situations. There are certainly pros and cons to each material type.

base layer - early bird gets the worm, or a summit bid all to ourselves in this...
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

Synthetic fabrics tend to be less expensive, a touch more durable, and pack down smaller. They also tend to hold onto moisture, retain odors over time, and often don't provide the same warmth-to-weight ratio when compared to their natural-fiber companions. Merino wool tops are typically more expensive and bulkier. But they offer benefits like superior body-temperature regulation, moisture-wicking ability, and odor resistance. Merino blends add positive characteristics like durability and stretchiness and can allow thinner fabrics to be made, but they're almost always more expensive than 100% wool. Silk, while incredibly valuable in terms of warmth-to-weight-to-thickness, is a hard sell based on durability alone.

base layer - less, sometimes, is more - if you&#039;re looking to go fast-and-light on...
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

The synthetic Cotopaxi Liso Top runs away with the competition regarding value. We found it tested high in most of our tests except absolute warmth: as a lighter-weight base layer, it excels. The Outdoor Research Echo Long Sleeve is also one of the most valuable synthetic layers on the market today. This top is versatile as a standalone shirt for activities like running and performs impressively well as a technical base layer. The Helly Hansen Lifa Stripe Crew is one of the least expensive base layers we've tested and would be a great choice to use for high-output activities in cold weather, like cross-country skiing. If you're value-minded but tend to run colder, 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.

base layer - the synthetic helly hansen lifa stripe crew is a worthy base layer...
The synthetic Helly Hansen Lifa Stripe Crew is a worthy base layer to wear under your kit during high output activities like cross country skiing or all alone like when you're off for a run.
Credit: Maddock Rigby

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 in the direction of what holds more importance for you as a buyer. Decide which metrics are most important for your sport or activity - whether it'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 important qualities to consider in your decision. 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 and also allow excess heat to escape when your heart rate climbs and body temperatures 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 and winter to test every quality that results in you successfully staying 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 Classic All-Season Merino 1/4 Zip, the Smartwool Classic Thermal Merino ¼ Zip, and the Meriwool Merino 250 Long Sleeve. These tops consist of thicker, cushy fabrics that seal in heat while maintaining excellent breathability and moisture-wicking abilities.

base layer - the smartwool classic all-season merino 1/4 zip&#039;s tightly knit...
The Smartwool Classic All-Season Merino 1/4 Zip's tightly knit fabric is surprisingly light and durable for a Merino wool blend.
Credit: Maddock Rigby

For the deep cold of winter, we recommend the SmartWool Classic Thermal Merino. As the heaviest 100% Merino layer we tested, this top is designed specifically with snow sports in mind. As an intriguing option to split the difference between light- and mid-weight, the Black Diamond Solution 150 Merino is as equally suited to working hard in the skin track as it is working all day in the snow. The Ortovox 185 Rock'N'Wool Long-Sleeve is a bit heavier than the Solution and is very similar in terms of offering a nice middle ground to split the seasons.

base layer - for some lightweight tops like the outdoor research alpine onset, a...
For some lightweight tops like the Outdoor Research Alpine Onset, a blend of synthetic fibers and all-natural Merino wool means that this crew will offer more warmth than its weight may suggest.
Credit: Aaron Rice

If you are looking for a layer that better suits highly aerobic activities or you want versatility across seasons, you will likely benefit from choosing a lighter-weight layer that is designed to breathe a bit better. Our testers' favorite aerobic layers are the REI Co-op Lightweight Crew and the Outdoor Research Echo — these tops are perfect for 3-season activities like backpacking or trail running. For cross-country and backcountry skiing, we would opt for the lightweight layers that still offer a bit of warmth, like the Outdoor Research Alpine Onset 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 Patagonia Capilene Air Crew or Icebreaker Merino 200 Oasis Half Zip, both of which provide a solid level of warmth but still offer impressive breathability.

base layer - the lofted merino wool blend of the patagonia capilene air crew has...
The lofted Merino wool blend of the Patagonia Capilene Air Crew has a unique webbed mesh material that traps air while allowing the fabric to breathe.
Credit: Maddock Rigby

There are some specific features that we've found to help keep us warm and may help you narrow your search for the perfect base layer. Models 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 top tucked in and snow out of our pants. But these design features can also keep your top from rising up and exposing your back and belly when bending over to put on your climbing skins or reaching for that next crimper when climbing.

base layer - the smartwool intraknit is impressively warm for its weight. what...
The SmartWool Intraknit is impressively warm for its weight. What you can't see is that our buddy is climbing in a puffy, while we had no problem hanging out for long-belays in the shade.
Credit: Jill Rice

The Argument Against Cotton


There are significant differences between a natural fiber (Merino wool, silk) and a synthetic fabric (polyester, polypropylene) when it comes to warmth. The key here is that they both continue to insulate when wet. Comparatively, cotton can absorb up to 100% of its material weight in moisture, leaving you wet, cold, and miserable, and thus could be quite dangerous in certain situations in the backcountry.

Breathability


Breathability is the yin to warmth's yang. Alongside warmth, it is arguably the most important quality of an effective base layer. Breathability is tied mainly to the moisture-wicking capability of a fabric. Effectively, this is the ability to collect moisture (sweat) and move that moisture to the outside surface of the fabric, where it can freely evaporate. The breathability of a garment is determined by how quickly and efficiently a fabric can convert sweat to free water vapor. A quality, breathable layer will help regulate your body temperature through a range of environments, regardless of your energy output. Depending on the situation, a great base layer will effectively work to keep you dry and warm, or dry and cool, depending on how it's designed.


Breathability is an extremely important quality during active pursuits, as well as stop/start activities like backcountry skiing 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. A non-breathable shirt will prevent that moisture from escaping, leading it to condense on the inside of the garment. This leaves you wearing a sweat-saturated shirt that is wet, heavy, and potentially dangerous in cold conditions.

base layer - the outdoor research echo l/s is the perfect top for long trail...
The Outdoor Research Echo L/S is the perfect top for long trail runs, or any heart-pumping activity through the warmer parts of shoulder seasons, or just chilly summer mornings.
Credit: Jill Rice

We assess each layer's breathability systematically to back up our findings after months of use hiking, running, skiing, climbing, and biking. We test each layer side-by-side in temperature-controlled indoor environments and use 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.

base layer - the patagonia capilene air proving its versatility, keeping us cool...
The Patagonia Capilene Air proving its versatility, keeping us cool and comfortable in the fall Utah Sun. Its nearly see-through fabric allows for air to pass through it with ease making it extremely versatile for conditions ranging from super cold when layered, to warm weather as a stand-alone layer.
Credit: Roland Mott

Not surprisingly, the tops that earn our highest scores for breathability are also made from the lightest weight fabrics. These include the Outdoor Research Echo L/S, Patagonia Capilene Cool Lightweight L/S, and REI Co-op Silk Crew. For warmer weather and high-exertion activities, these are some base layers to consider closely.

Several warmer options made of a Merino blend allow lightweight yet strong fabrics to be spun up into beautifully breathable baselayers. These include the 150 g/m² Outdoor Research Alpine Onset 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 when layering up for colder conditions while keeping relatively dry and fresh.

base layer - the rei co-op merino 185 long-sleeve half-zip is an excellent merino...
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


When choosing between options, comfort and fit are usually at the top of the list for many consumers. If a layer excels in all other categories but fits you poorly or is uncomfortable, it won't serve you. This may be the toughest metric to rate because comfort and fit are ultimately subjective and are different for everyone's preferences and body type. We try our best to give as subjective an opinion as possible when considering all the factors that play into a layer's comfort and fit. We scrutinize each layer and ask the following questions: How does the fabric feel next to your 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.


The Black Diamond Solution 150 Hoody reaches the echelons of our ratings for slim, athletic-fit base layers. What sets it apart from the pack is its Merino wool fabric, which we found to be thin yet soft. Long sleeves with thumb holes and a drop tail hem keep even taller people covered when reaching for those distant hand holds on the warmup route. If you're looking for a similarly weighted athletic fit base layer without the 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 — especially helpful when you layer up and want to avoid pinch points.

base layer - the solution hoody features a tight, athletic, next to skin fit.
The Solution Hoody features a tight, athletic, next to skin fit.
Credit: Nikki Shegda

For ultimate stretch with surprising softness, the Cotopaxi Liso Top delivers. The extra long sleeves with thumb loops and a loose fit accommodate any acrobatic stylings without feeling baggy. As a synthetic, it may rival the comfiness of many Merino options. 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 load in your pack.

base layer - the stretchiness of the cotopaxi liso&#039;s fabric equates to total...
The stretchiness of the Cotopaxi Liso's fabric equates to total freedom of movement, even when stacked underneath multiple mid and outer layers.
Credit: Justin Simoni

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 zipped down gets it out of the way when you need some fresh air to circulate. The sleeves are perfectly sized to allow you to roll them up past the elbows and shoulder panels, and the flatlock seams have been moved off the crest of your shoulders. The Ortovox 185 Rock'N'Wool Long-Sleeve also gets five stars for being soft and comfortable next to the skin and is a perfect pick if you're looking to wear something a little lighter.

base layer - the smartwool classic thermal merino &frac14; zip&#039;s high collar rests...
The Smartwool Classic Thermal Merino ¼ Zip's high collar rests comfortably at the chin line
Credit: Justin SImoni

Shop Local


If possible, we always suggest trying garments on in person, as it is the only way to know whether it will fit you well. This also saves you the time, hassle, and carbon impact of shipping and returning.

Durability


Durability is a characteristic that we search for in all of our outdoor gear: we often spend more on high-quality products to own less 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 that we apply to all of our consuming 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 made in some part with recycled fibers.


To test durability, we inspect the strength of the fabrics, the quality of the stitching, and the construction of the pieces as a whole. We also drag them up against rocks, roll them in the dirt, bushwack through manzanita and chaparral to get to beautiful places, and subject them to merciless amounts of washing and drying cycles. 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 the fabrics fair (think wash-board technique). This specific test gives us a very clear idea of how certain tops will hold up to long-term abrasion.

base layer - making its way up an eldo classic, the smartwool classic shows off...
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

In general, our test results show that base layers made of thick synthetic fabrics are found to be the most durable. In contrast, 100% Merino wool base layers — no matter the thickness — tend to test as the least durable. Some base layers are made with a Merino wool blend with polyester, nylon, and/or elastane spun with the wool fibers. The higher percentage of other materials blended in, the more durable the fabric becomes. But, the durability never matches a pure synthetic. Thin fabrics, no matter the fabric type, show lower results in our durability tests.

base layer - synthetic material has the tendency to drop seams after repetitive...
Synthetic material has the tendency to drop seams after repetitive use, but with no actual damage to the face fabric; flat-lock seams hold the tough Outdoor Research Echo L/S together.
Credit: Jill Rice

The Under Armour ColdGear Base 4.0 — a thick synthetic — was our absolute standout, seemingly unaffected by our harsh abrasion test. It would make a good choice for those doing heavy work outside. Both the Cotopaxi Liso and Helly Hansen Lifa Stripe Crew — two other lighter synthetics — 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: the Smartwool Classic All-Season scored best and should more than suffice for most activities if worn under a more durable layer and cared for properly when washing.

base layer - for cold conditions outside, the under armour coldgear base 4.0...
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 wool and silk, historically, are notorious for their lack of durability. Both tend to wear holes through quickly and/or shrink and lose their shape after repeated washings. Merino wool has come a long way in terms of durability — particularly considering wool/polyester blends. But when it comes to longevity, natural material still falls behind its 100% synthetic counterparts. For a lot of folks, the performance benefits of Merino wool outweigh the lack of durability, and if you take proper care of your Merino top, it can serve you for a long time. Despite its reputation as being a relatively short-term fabric, several of our testers have gotten many years of use out of theirs. That said, they try to be careful to hang dry them and not wear them every single day (they are certainly comfortable enough to want to do just that in the winter).

base layer - durability is paramount for base layers that are going to pull...
Durability is paramount for base layers that are going to pull double-duty as standalone shirts for rugged activities like mountain biking.
Credit: Jill Rice

Merino Care


Although some Merino wool garments give the OK to tumble dry on low, we suggest washing on a cold cycle and laying to flat 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


Staying dry is a foundation of being comfortable in the outdoors. Not only can a wet top severely inhibit your ability to find happiness and joy, but it can also be downright dangerous under the wrong conditions. Sometimes the moisture comes from outside sources, like 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 left out to dry. But based on our collective experience, we do expect a strong correlation between drying speeds 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.

base layer - when the going gets tough, its important to have a base layer, like...
When the going gets tough, its important to have a base layer, like the Patagonia Capilene Cool Lightweight, that will actively dry out on your body.
Credit: Jill Rice

Our drying speed test is a simple one. We run all our base layers on a wash cycle, then hang them out, periodically checking when they're completely dry. We give slightly more significance in our scores to thicker base layers that we find have dried at the same time as thinner base layers. To precisely gauge how dry these fabrics have reached during our tests, we weigh the tops to determine how much water is still retained in the garment, rather than relying solely on feel, and then we compare this to the dry weight.

base layer - colorful and practical, our soak n&#039; dry test seeks to replicate how...
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

Thinner fabrics dry faster than thicker ones. The REI Silk Crew dries lightning-fast, as does the Patagonia Capilene. Cool Lightweight. We were also pleased with the dry times when hanging the Cotopaxi Liso off our pack on a crisp, sunny autumn day in the backcountry.

base layer - once hand-washed in a creek, rung, and hung off our pack, the...
Once hand-washed in a creek, rung, and hung off our pack, the Cotopaxi Liso dried fast enough to be ready to be worn once in town for pizza and ice cream.
Credit: Justin Simoni

Merino wool claims that it can 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 these layers alone in wetter, more mild climates.


The Merino wool/polyester blend of the Black Diamond Solution 150 Merino Hoody does a great job at resisting moisture absorption. We personally experienced hand-washing this garment in a bubbling creek, hand-wringing it, and wearing it out while backpacking, to have it dry to the touch within an hour.

base layer - the solution hoody dries so fast that after washing and carefully...
The Solution Hoody dries so fast that after washing and carefully ringing it out, we simply wore it for an hour on a warm afternoon while enjoying our backpack out.
Credit: Justin Simoni

A surprising finding in our dry test was the Under Armour ColdGear Base 4.0, the thickest synthetic we tested. Despite being so thick, its dry times were more similar to 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.

base layer - consider when and how you plan to use your base layer. choosing a...
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


The ability to layer well is an often overlooked consideration but is important for practical outdoor use. One of the greatest qualities of a base layer is its versatility to be worn as a standalone top or to be layered in a myriad of ways to keep you warm and comfortable in any temperature or situation.


To test layering ability, we consider all the ways a top can be layered, and we try all of the combinations with every 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.

base layer - an example of a layering system. base layer, fleece mid layer, soft...
An example of a layering system. Base layer, fleece mid layer, soft shell, and down puffy. The Patagonia Capilene Air, pictured here, traps heat extremely well in a layering system but as a stand-alone layer, air cuts right thru it.
Credit: Roland Mott

Most impressive in this metric was the Black Diamond Solution 150 Merino Hoody, which comes packed with more features than any other base layer we've tested: thumb loops, long sleeves you can roll up, a hood, and a front zip all provide a plethora of options to regulate temperature. The stretchy and soft Merino wool blend and athletic fit make this an easy top to layer on top of also.

base layer - with a hood, thumb loops, sleeves that can be rolled up past the...
With a hood, thumb loops, sleeves that can be rolled up past the elbow, and a front zip, the Black Diamond Solution 150 Hoody almost performs like two layers in one.
Credit: Justin Simoni

For a warmer option, the Smartwool Classic Thermal Merino is both handsome and functional. The quarter zip and cuffs that are loose enough to roll up aid in regulating temperature. Its more casual fit means you'll most likely want to wear another base layer underneath for added warmth on the coldest days. The Smartwool Intraknit Thermal lacks a front zipper, but the Merino blend lofts up well to be warm yet light all on its own, or it can easily be layered with something else.

base layer - the midweight intraknit layers well with other performance-type...
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

For lighter synthetics in warmer weather, the Outdoor Research Echo is ready to be worn on an all-day hike as a sun shirt as well as your base layer under a jacket while you wait for more sunshine and warmth. Another solid choice is the Cotopaxi Liso Top, which is looser, stretchier, and warmer. Both of these layers are super easy to layer underneath almost anything, and the Liso also has thumb loops to help you slide un-bunched into your fleece or puffy.

base layer - the outdoor research echo l/s works great as a warm weather base...
The Outdoor Research Echo L/S works great as a warm weather base layer perfect for those temperate late autumn afternoons.
Credit: Drew Crittenden

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. It's important for you 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.

Aaron Rice and Justin Simoni


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