Reviews You Can Rely On

The 5 Best Base Layers of 2024

We tested men's base layers from Smartwool, Patagonia, Black Diamond, Icebreaker, REI, and more to find the warmest and most comfortable options
gearlab tested logo
Best Base Layer Review (Our team has tested a lot of base layers over the years, and are equipped to offer expert advice to help you find the...)
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
Wednesday April 24, 2024

For over a decade, our team of experts has bought and tested dozens of the best base layers on the market. For this update, we compare 16 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 warmest and best fleece jackets to keep you toasty.

Editor's Note: This review was updated on April 24, 2024. We added new products from REI, and more product suggestions as alternatives to our award winners.

Related: Best Base Layers for Women

Top 16 Base Layers - Test Results

Displaying 6 - 10 of 16
 
Awards   Best Buy Award   
Price $85.93 at Amazon$100 List
$79.99 at Amazon
$60 List
$59.99 at Amazon
$90 List
$62.89 at REI
$59 List
Overall Score Sort Icon
75
74
73
73
72
Star Rating
  • 1
  • 2
  • 3
  • 4
  • 5
  • 1
  • 2
  • 3
  • 4
  • 5
  • 1
  • 2
  • 3
  • 4
  • 5
  • 1
  • 2
  • 3
  • 4
  • 5
  • 1
  • 2
  • 3
  • 4
  • 5
Pros Front zip with high collar, gusseted underarms enhance comfort, drop tail hemTough and thick fabric, fast drying for the weightAffordable, very warm, fashionable fit, breathableSoft, stretchy 100% Merino wool, underarm gussets, front 1/2 zipUltralight, airy and breathable, affordable, 100% recycled polyester
Cons Tight knit wool lacks durability, slower dry times, slim fit may not work for everyoneThick fabric with slim fit leads to pinch points, sleeves not long enough for thumb loops, many seams stick outFiner thread Merino is not quite as durable, slightly itchy, shoulder top seamsLarge amount of merrow stitching, prone to loosing shape after repeated washings, durability issuesNot a warm layer by itself, loose-fitting cuffs can get caught up when layering
Bottom Line This solid base layer features a front zipper, a tight athletic fit, and a good amount of warmth for its weight due to its 100% Merino wool constructionA thick synthetic base layer good for dirty outside jobs from chopping wood to building housesThis top delivers the fine qualities of a Merino wool base layer without the extreme costThis athletic fitted, warm, super soft 100% Merino wool base layer is a great choice for cold weather activities, just care for it thoughtfullyA high-value piece whose breathability and airy fit means that it can be worn for high-output activity regardless of the season, but not your go-to layer for mid-winter warmth
Rating Categories Icebreaker Merino 2... Under Armour ColdGe... Meriwool Merino 250... REI Co-op Merino 18... Patagonia Capilene...
Warmth (25%)
8.0
7.0
7.0
9.0
4.0
Breathability (20%)
7.0
6.0
8.0
7.0
9.0
Comfort and Fit (20%)
8.0
7.0
8.0
7.0
8.0
Durability (15%)
7.0
10.0
6.0
5.0
7.0
Drying Speed (10%)
7.0
9.0
7.0
9.0
10.0
Layering Ability (10%)
7.0
6.0
7.0
6.0
7.0
Specs Icebreaker Merino 2... Under Armour ColdGe... Meriwool Merino 250... REI Co-op Merino 18... Patagonia Capilene...
Measured Weight (Size Large) 9.0 oz 10.6 oz 8.6 oz 10.1 oz 3.8 oz (size medium)
Measured Shirt Length (Size Large) 28 in 29 in 30 in 26.5 in 29 in (size medium)
Material 100% Merino wool 78% polyester, 22% elasterell RWS Merino wool 100% Merino wool 2.3 oz 100% recycled polyester double knit
Fabric Weight Class Midweight Midweight Midweight Midweight Ultra Lightweight
Fit Slim fit Slim fit Slim fit Slim fit Slim fit
Thumb Loops No Yes No No No
Air Dry Test 60 min 40 min 65 min 40 min 30 min
Dryer Safe No Yes No No Yes
Odor Control Fabric Naturally odor resistant UA Scent Control Technology Naturally odor resistant Naturally odor resistant HeiQ® Mint odor control
UPF Sun Protection None listed None listed 50+ 30 None listed
Seam Stitching Flatlock seams Various Flatlock seams Flatlock and flat seams Flatlock seams
Shoulder Top Seams Yes No Yes No (rolled forward design) Yes
Drop Tail Hem Yes No No No Yes
Available Cuts Crew, short-sleeve, 1/2 zip Crew, 1/4 zip Crew, 1/2 zip Crew, 1/2 zip, short-sleeve, tall Crew, short sleeve


The Best Base Layers for 2024


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
High price
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 moves the seamlines so they don't chafe when wearing a backpack. 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 tested.

Since this top excels in colder conditions, 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, and pick out a more appropriate base layer to be comfortable in instead. We like Smarwool's Classic All-Season Merino option for when the 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.

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

For snowy missions in the mountains, the Smartwool Classic Thermal Merino 1/4 Zip is the base layer we instinctively grab.
Credit: Justin Simoni

Best Synthetic Bang for Your Buck


REI Co-op Midweight Half-Zip


75
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 7.0
  • Comfort and Fit 8.0
  • Durability 8.0
  • Drying Speed 7.0
  • Layering Ability 8.0
Material: 92% Polyester, 8% Spandex| Weight: 10 ounces, size L
REASONS TO BUY
Dries quickly
Soft fabric
Thumb Holes
REASONS TO AVOID
Warmth is slightly less than wool
Soft fabric can get caught on mid-layer

Those looking for the best value for their hard-earned cash or just want a little more money for after-adventure pizza should take a serious look at the REI Co-op Midweight Half-Zip, which performs solidity across the board in our tests. Its 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, meaning your perspiration gets a chance to leave your skin. 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.

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 options that have a deeper list of features. But for the price, this base layer does pull off the very difficult trick of working really well in a wide variety of conditions which all but adds even more value to this top. The Icebreaker Merino 200 Oasis Half Zip is another partial zip option that scores on par with the REI. It is just as comfortable, but slightly less durable.

Read more: REI Co-op Midweight Half-Zip review

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

Best Value for Merino


Meriwool Merino 250 Long Sleeve


73
OVERALL
SCORE
  • Warmth 7.0
  • Breathability 8.0
  • Comfort and Fit 8.0
  • Durability 6.0
  • Drying Speed 7.0
  • Layering Ability 7.0
Material: 100% Merino wool | Weight: 10.1 oz
REASONS TO BUY
Affordable
Balances warmth and breathability
Stylish
REASONS TO AVOID
Slightly itchy
Less durable

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 initially 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. If you're seeking an ultra-durable base layer, the synthetic Under Armour ColdGear Base 4.0 Crew is worth checking out.

Read more: Meriwool Merino 250 Long Sleeve review

The Meriwool Merino 250 Long Sleeve fits comfortably loose.
Credit: Justin Simoni

Most Versatile Base Layer


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 Solution is a solid 150 g/sm Merino wool blend that hits a sweet spot between a light and mid-weight layer. It has a helmet-compatible hood, half-zip, and extra long sleeves with thumb loops — all of which help you cover up or expose some skin depending on the conditions. 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 go 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 is a thin, stretchy fabric, but durability is a concern if worn alone and not safely underneath a top layer. If you'd rather invest in a more durable layer, the Ridge Merino Aspect Midweight is a similarly weighted, blended, hooded model to compare this against. It's also important that we talk about the price of the Solution 150: this is one of the most expensive base layers we've tested. Still, if you can swing the cost, 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

Snow and sun, the Black Diamond Solution 150 Merino Half Zip Hoody meets the demands you press it into action.
Credit: Justin Simoni

Best Midweight Layer


Smartwool Intraknit Thermal Merino


75
OVERALL
SCORE
  • Warmth 7.5
  • 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 elbow protection
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 pilling of the Merino wool blend than we'd like to see on a base layer of this price. The higher price point alone may be enough to dissuade you from purchasing this one. Also, its slim fit may be too tight for comfort, especially around the shoulders, where pinch points can develop when worn under additional layers. The Patagonia Capilene Cool Lightweight L/S is a bit more forgiving in terms of overall fit. 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

We loved the Smartwool Intraknit Thermal Merino for active days when we needed to be able to easily add and remove layers when transitioning from cool to cold conditions and sometimes back again.
Credit: Justin Simoni

Compare Products

select up to 5 products to compare
Score Product Price
80
Smartwool Classic Thermal Merino 1/4 Zip
Best Overall Base Layer
$120
Editors' Choice Award
77
Black Diamond Solution 150 Merino Half Zip Hoody
Most Versatile Base Layer
$145
Top Pick Award
77
Smartwool Classic All-Season Merino 1/4 Zip
$95
75
REI Co-op Midweight Half-Zip
Best Synthetic Bang for Your Buck
$60
Best Buy Award
75
Smartwool Intraknit Thermal Merino
Best Midweight Layer
$130
Top Pick Award
75
Icebreaker Merino 200 Oasis Half Zip
$115
74
Under Armour ColdGear Base 4.0 Crew
$100
73
Meriwool Merino 250 Long Sleeve
Best Value for Merino
$60
Best Buy Award
73
REI Co-op Merino 185 Long-Sleeve Half-Zip
$90
72
Patagonia Capilene Cool Lightweight L/S
$59
71
Ridge Merino Aspect Midweight Merino Balaclava Hood
$90
71
Outdoor Research Alpine Onset Merino 150 Crew
$99
70
Helly Hansen Lifa Stripe Crew
$45
68
Ortovox 185 Rock'N'Wool Long-Sleeve
$110
67
Outdoor Research Echo Long Sleeve
$52
66
REI Co-op Lightweight Long-Sleeve Crew
$40

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

How We Test Base Layers


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 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)

We hands-on tested these base layers to ensure we found the best of the best.
Credit: Justin Simoni

Why Trust GearLab


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. 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. 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.
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. 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 your own personal needs will dictate which metrics are most important to you. 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'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

We've been very impressed with the REI Co-op Midweight Half-Zip with the amount of value it provides. It's fairly heavy 220 g/sm is good enough for wintry excursions, and its price tag will allow you a budget for some aprés 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 Outdoor Research Echo Long Sleeve is also one of the most value-packed 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 more affordable base layers we've tested and is a great layer 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 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 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, Winter, and Spring 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. We also tested them indoors in our pop-up labs to compare them in as similar conditions as we could. The standout tops for well-balanced warmth are the Season Merino 1/4 Zip, the Classic Thermal Merino 1/4 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 - 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

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.

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

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. Also take a look at the Ridge Merino Aspect Midweight Merino Balaclava Hood which is hooded and has thumb loops, similar to the Solution 150. 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

Those seeking a layer for highly aerobic activities or versatility across seasons will likely benefit from choosing a lighter-weight, more breathable layer. Our testers' favorite aerobic layers are the REI Co-op Lightweight Long-Sleeve Crew and the Outdoor Research Echo, which 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 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 provide a solid level of warmth but still offer impressive breathability.

base layer - the outdoor research echo is perfect for active pursuits, like...
The Outdoor Research Echo is perfect for active pursuits, like warming up on the spray wall before hitting up your climbing project.
Credit: Nikki Shegda

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 shirt tucked in and snow out of our pants. 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. 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.

base layer - as well as an extra long hem on the front and back, the ridge merino...
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 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 and 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 outdoor research alpine onset - at only 150 g/sm - makes a...
The Outdoor Research Alpine Onset - at only 150 g/sm - makes a breathable wool blend baselayer for high output activities, like a crisp Fall jog before work.
Credit: Jill Rice

Not surprisingly, the top that earn our highest scores for breathability - the Outdoor Research Echo L/S - is also made from the lightest weight fabrics. 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 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 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 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 are dictated by preference 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 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.

new photo here

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 1/4 zip's high collar rests...
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

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, bushwhack 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 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 wool fibers. The higher the 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. 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 as well as all-day movie-watching sessions. 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. The Smartwool Classic All-Season also scored as one of the most durable blended tops we tested and should 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 regarding longevity, natural material still falls behind its 100% synthetic counterparts. For many 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 a relatively short-lived 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 the care instructions on some Merino wool garments give the okay to tumble dry 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


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 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 - thinner base layers like the ridge merino aspect midweight merino...
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 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. Thinner fabrics dry faster than thicker ones. Our tests revealed that thinner, synthetic shirts like the Patagonia Capilene Cool Lightweight L/S dry super quickly.

Lightweight synthetic base layers like the Patagonia Capilene Cool Lightweight Long Sleeve may not retain as much warmth, but do dry very quickly.
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.

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 its thickness, its dry times were more similar to a thinner, midweight layer. The Layer Half-Zip is almost as thick, but also dries also as quick. 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, where a light, tight-fitting base...
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

One of the 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. Thanks to the stretchy and soft Merino wool blend and athletic fit, it's easy to toss a layer on top.

On long, strenuous climbs, we appreciated being able to zip down the Black Diamond Solution 150 Merino Half Zip Hoody and roll up the sleeves to let some warmth escape, rather than having to stop to take off the layer completely.
Credit: Justin Simoni

Another standout for its layering ability is the Ridge Merino Aspect. Its balaclava hood adds coverage and stores away easily, staying out of the way of your other layers. The extra long sleeves are anchored by thumb loops, 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 that are loose enough to roll up aid in regulating 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 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. It's super easy to layer underneath almost anything.

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. 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.

Justin Simoni, Aaron Rice