Reviews You Can Rely On

Best Base Layer for Women of 2021

We put women's base layers to the test from Smartwool, Icebreaker, Carhartt, Patagonia, and more to find the warmest and most versatile options
A look at a few of the base layer tops we've tested.
Photo: Amber King
Wednesday November 3, 2021
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Over 7 years, our lady experts have bought and tested 32 of the best women's base layers available. This 2021 review features 14 of the market's best options that we continuously test side by side. Testing across the globe, we have sailed high seas, scaled thousand-foot cliffs, skied multiple mountain ranges, run ultra-distance miles, and camped everywhere in between. Our team assesses each top across key performance factors like comfort, warmth, and breathability. Our field and in-house tests provide the insight and expert advice to help you find a next-to-skin layer that performs to meet your needs.

Top 14 Product Ratings

Displaying 1 - 5 of 14
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Awards Editors' Choice Award Editors' Choice Award   Best Buy Award 
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$50 List
$49.99 at Amazon
Overall Score
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72
74
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Pros Wide range of thermoregulation, cozy materials, no odor after long wear, longer fit through torso and arms, versatileCozy fleece interior, easy to layer, warm, versatile, stash pocket, tight fitGreat thermoregulation, exceptional at wicking, impressive durability, least itch factor of all wool tops testedImmensely comfortable, quick to dry, lightweight, huge range of thermoregulation, no smellWarm, durable, breathable, thumb loops, 1/4 zip design vents well, excellent value, no odor
Cons Stretches after wearing for several days, thick construction isn't ideal for warmer daysMore expensive, not super breathableNot very cozyLacks durability, expensive, harder to layerNeed to size up on fit, shorter torso and arm length
Bottom Line This top provides cozy comfort, top-notch thermoregulation, and resists odor build-up better than any model we testedThis high performance synthetic layer is ready for pretty much any adventure you dream upThe most comfortable wool was used in this lightweight base layerAn amazing balance of breathability and warmth with some layering issuesA good looking blended polyester and merino wool top that outperforms its price tag
Rating Categories Smartwool Merino 25... Arc'teryx Rho LT Zip Icebreaker Merino 2... Patagonia Capilene... Carhartt Force Heav...
Warmth (25%)
9.0
8.0
9.0
8.0
8.0
Breathability (25%)
7.0
6.0
7.0
9.0
7.0
Comfort And Fit (20%) Sort Icon
9.0
9.0
8.0
8.0
7.0
Layering Ability (20%)
6.0
8.0
7.0
4.0
7.0
Durability (10%)
8.0
9.0
7.0
5.0
8.0
Specs Smartwool Merino 25... Arc'teryx Rho LT Zip Icebreaker Merino 2... Patagonia Capilene... Carhartt Force Heav...
Fabric Weight Midweight (250 g/m²) Midweight Midweight (200 g/m²) Midweight (147 g/m²) Midweight
Measured Weight (size) 8.3 oz (small) 7.1 oz (small) 5.8 oz (small) 5.1 oz (small) 6.8 oz (med)
Material 100% merino wool Torrent 190 with Polygiene (84% polyester/16% elastane) 100% merino wool 51% merino wool/49% recycled polyester seamless zigzag knit comprised of 18.5-micron-gauge lofted wool 80% polyester, 20% wool
Cuts avaliable Crew, 1/4 zip 1/4 zip Crew, 1/2 zip neck Crew, hoody 1/4 zip
Odor Control Fabric Naturally odor resistant Polygiene Naturally odor resistant Naturally odor resistant Naturally odor resistant
Thumb Loops? No No No No Yes
UPF (Sun Protection) No No No No N/A
Length (short, medium, long) Medium Medium Medium Medium Medium
Fit (Based on 5'7, 140-lb woman wearing size small) Fitted (not tight), true to fit. Trim fit Fitted (not tight), true to fit. Fitted (not tight), true to fit. Fit is small, size up
Accessory Pocket? No Yes No No No
Flat-lock seams (prevents chaffing) Yes Yes Yes Yes Yes


Best Overall Women's Base Layer


Smartwool Merino 250 1/4 Zip - Women's


78
OVERALL
SCORE
  • Warmth 9
  • Breathability 7
  • Comfort and Fit 9
  • Layering Ability 6
  • Durability 8
Materials: 100% merino wool | Thickness: (250 g/m²)
Incredibly comfortable
Thermoregulation range
Great wicking power
Comfortable fabrics
Not super durable
Stretches out after multiple days of use

Wear this super comfy midweight top from the trail to your bed. The Smartwool Merino 250 ¼ Zip has fantastic comfort and versatility. Loaded with 100% natural Merino wool fibers, it provides one of the most extensive ranges of thermoregulation tested. It functions well as a long underwear top and a wear-alone top in temperatures ranging from the double negative digits to highs of 70 degrees Fahrenheit. It outperforms almost every other shirt in this review for its ability to keep us dry and comfortable when conditions go from warm to cold and wet to dry. The fabric wicks away moisture, dries quickly when on, and doesn't stink.

While the fabric is soft and cozy, the only thing that it truly lacks is durability against abrasive activities when worn without a layer over top.

Though the fabric is thick and stands up to normal wear and tear, we have noticed that this top can stretch out after multiple days of use. However, it will bounce right back into shape after being thrown into the dryer. We consistently recommend this top to our female friends for its immensely cozy fabric, excellent quality, and outstanding thermoregulation.

Read review: Smartwool Merino 250 1/4 Zip - Women's

Best Synthetic Base Layer


Arc'teryx Rho LT Zip - Women's


78
OVERALL
SCORE
  • Warmth 8
  • Breathability 6
  • Comfort and Fit 9
  • Layering Ability 8
  • Durability 9
Materials: 84% polyester, 16% elastane | Thickness: Midweight
Fleece-lined to keep you cozy and warm
Fitted design is easy to layer
Stash pocket for a key or energy gel
Durable and well-crafted
Lacks some breathability
Expensive
Holds more odor than merino fabric

We've tested the Arc'teryx Rho LT Zip over the last seven years (with a few updated version in between), and it still stands out as our go-to synthetic for all technical missions. The interior is fleece lined with wicking power that does a good job moving moisture. We love the fitted design that is stretchy and incredibly easy to layer over and even under, plus the zippered neck for optional ventilation. It's one of the most versatile base layer tops we've tested, performing well from ski tours in Colorado to mega rafting missions in the Grand Canyon. As is true with most synthetics, the wear and tear is minimal, even after years of being put through the wringer. Tried, tested, and truly awesome.

To benefit from the increased levels of comfort and warmth due to the fleece lining on the interior of this base layer, you must sacrifice a certain amount of breathability. We suggest using this drawback to your advantage and wearing this layer as a stand-alone piece during the change of season to create a barrier between your sensitive skin and those cold north winds. This layer is more expensive than other synthetic options, however, given that this is one of the most time-tested pieces that we've had the opportunity of using, the value of performance you get out of it is definitely worth the investment. This layer is best for a woman that is seeking a synthetic layer that's durable, technical, and looks great.

Read review: Arc'teryx Rho LT Zip - Women's

Best Bang for Your Buck


Carhartt Base Force Heavyweight 1/4 Zip - Women's


74
OVERALL
SCORE
  • Warmth 8
  • Breathability 7
  • Comfort and Fit 7
  • Layering Ability 7
  • Durability 8
Materials: 80% polyester, 20% merino wool | Thickness: Midweight
Excellent thermoregulation
Maintains shape after heavy use
Durable construction
Excellent comfort features
High value
Sizing up is recommended

When we chose the Carhartt Base Force Heavyweight 1/4 Zip as part of our testing fleet, we expected the strong durability and functionality that this manufacturer is known for. Still, we were surprised when this base layer exceeded our expectations and became one of the top performers. It feels just as soft as merino wool. It also wicks well and offers durable construction, similar to a 100% synthetic top. When wearing it for many days on end, without washing it, the materials didn't build up odor nor did the layer stretch out. Furthermore, its thermoregulation is very impressive. It wicks well and efficiently moves moisture. While Carhartt calls it "heavyweight," our team agrees that it is similar in performance to other midweight options on the market. The price is right, too — it's hard to find a product this high in value, especially considering that it features the convenient (and commonly more expensive) quarter zipper on the neck and chest.

The only thing that we've added to our wishlist for this top is a size adjustment. The materials are a bit stiffer than 100% merino wool, meaning the fabric doesn't stretch as much. The length through the arms and torso is about medium, but because it doesn't stretch, you can't pull the arms to get a little longer, which is also true for the torso. For fit, sizing up was key for our lead tester. All in all, if you're seeking a stellar deal for an all-around awesome polyester-wool base layer, this one can't be beat for the price.

Read review: Carhartt Base Force Heavyweight 1/4 Zip - Women's

Best for Lightweight Breathability


Odlo Kinship Light Crew - Women's


71
OVERALL
SCORE
  • Warmth 5
  • Breathability 8
  • Comfort and Fit 7
  • Layering Ability 9
  • Durability 6
Materials: 84% Tencel (lyocell), 16% polyamide | Thickness: Lightweight
Ultralightweight fabric
Enhanced breathability and ventilation
Easy to layer due to snug fit
Not as warm
Not as durable as thicker fabrics

The Odlo Kinship Light is an excellent option for the athlete seeking ultralight breathability and performance throughout the year. Constructed from 84% eco-friendly Tencel (a brand name for lyocell) and 16% polyamide, this base layer offers another option besides polyester and merino wool. While nowhere near the warmest base layer that we tested, that's the intention with this top made for high-output activity. The ultralight fabric does retain some heat that you generate through activity, but it's more impressive how it wicks away moisture and ventilates through its aesthetically pleasing ventilation graphics. It's a great option for trail runs during the change of season or nordic skis where your body will be in motion.

While we never experienced any durability issues with this layer (even while climbing through a chimney or two), we suspect that this layer may not last as long as its thicker competitors. Worn as intended as a first layer under another top or jacket, though, and abrasion risk becomes less of a factor. If you are looking for an ultralight and versatile layer that breathes well and offers superior ventilation, the Odlo Kinship Light is a hi-octane option at an affordable price.

Read review: Odlo Kinship Light - Women's

Compare Products

select up to 5 products to compare
Score Product Price Our Take
78
$105
Editors' Choice Award
Comfort and excellent thermoregulation with quality construction
78
$125
Editors' Choice Award
Versatility and cozy comfort all in one well-built synthetic package
77
$95
A lightweight base layer that packs in amazing comfort and versatility
74
$50
Best Buy Award
A high value contender built to take on the elements of all seasons
72
$85
A light base layer built to breath and wick away sweat
72
$59
A high value synthetic base layer that should be considered for high output activities
72
$129
Layering issues aside, it's one of the warmest and most breathable base layers out there
71
$80
Top Pick Award
An ideal top for heavy exertion because it dries fast and offers excellent breathability without adding too much warmth
70
$110
If not for the unnecessary and uncomfortable seams, we would more readily recommend this top that thermoregulates well
65
$50
A nice, lightweight base layer that won't empty your wallet
65
$80
While we respect the lower price offering of this top, it failed to impress our testers in any significant area of performance
59
$50
Versatile with great value and a synthetic construction
58
$110
A super durable merino wool contender with cute design and style
56
$50
A silk top that is both stylish and breathable

The Icebreaker Oasis 200 was just what we needed to stay warm and...
The Icebreaker Oasis 200 was just what we needed to stay warm and dry during this fall training run in Indian Creek.
Photo: Toby Swimmer

Why You Should Trust Us


Our testing team is led by Amber King and Trish Matheny. As a seasoned gear reviewer, she spends her time backpacking into remote places, canyoneering through slots deep in the earth, and finding cool trails to run worldwide. Hardcore women she meets along her adventures become additional testers to provide unbiased, diverse, and genuine feedback on all base layer tops tested. After spending over a decade in the Tetons, Trish Matheny knows what she's looking for in base layer performance. An avid trail runner and rock climber, Trish wears base layers frequently while climbing thousands of vertical feet and on long-distance trail runs in cool to cold weather in the Sierra Nevada Mountains, her current home.

Click to enlarge
Click to enlarge
Click to enlarge

The base layer tops we test are used at a minimum for three months, and we continue to test them until they see an update throughout the year. When making our selection, we take hours researching the best options on the market before selecting the very best and subjecting them to our rigorous side-by-side testing plan. We wear them everywhere we go. We've tested across the world, from the high glaciers of Alaska to the rainy and cool landscapes of Iceland. We take these tops trail running, backpacking, rafting, climbing, backcountry splitboarding, and hiking to determine how each performs during unique experiences in the backcountry. Once we complete our field testing, we evaluate the durability of each layer, noting any tears or snags. Finally, we score across the same metrics to offer a comparative assessment based on our experience.

Related: How We Tested Base Layer for Women

Analysis and Test Results


A base layer top is an integral part of any women's outdoor wardrobe. This piece sits closest to the skin, wicks away moisture, and ultimately keeps you warm and comfortable while tackling summits or lounging around the chalet. The base layer tops we chose are composed of either synthetic materials, merino wool, or a blend. No tops in this review contain cotton. Throughout testing, we rate each product using five key metrics: warmth, breathability, comfort & fit, layering ability, and durability.

Related: Buying Advice for Base Layer for Women


Value


Wondering which top offers the best performance relative to its price? We understand the importance of return on your investment. Typically, the largest trade-off in this category lies in the materials used. Merino wool tends to cost more money than synthetic fabrics, and this higher price is passed on to the consumer. The Roman Trails Outfitters top is a merino top that retails for almost 50% less than our top performers. However, its thin materials stretch out over time and you end up sacrificing durability.

Our favorite value-based purchase of all models tested is the Carhartt Base Force Heavyweight 1/4 Zip. This synthetic and merino wool blend shirt is similar to our top performers and does an amazing job in the field for a fraction of the price. However, it's also worth considering the long-term value of tops like the Arc'teryx Rho Lt. Its superior craft and quality lead to season after season of use, which reduces its total cost over time.

Our experts find testing the market&#039;s top products for the outdoors...
Our experts find testing the market's top products for the outdoors to be fun, especially when our expert canines come along for much-needed assistance.
Photo: Amber King

Warmth


How many times have you started hiking, only to start sweating, then begin to shiver once you slow your pace? The base layer tops that offer the highest level of warmth are those that can offer warmth during intense activity like nordic skiing as well as riding the chairlift. Different tops offer different fabric weights, which contributes to overall warmth. In general, if you know you're going to be sitting around in cold weather, choose a thicker option. If you think you're going to be moving a lot more with minimal breaks in cold weather, choose a thinner option to avoid overheating. A midweight base layer is typically a good compromise.


During our testing, we only reviewed lightweight and midweight models. Keep in mind that most of the options listed here have different weight options. If you like the way a top sounds, check to see what other fabric weights are available.

The Arc&#039;teryx Rho LT offers stand-alone warmth with its cozy...
The Arc'teryx Rho LT offers stand-alone warmth with its cozy fleece-lined interior. Here we explore the stunning glaciers of Alaska on a 10-mile ski touring mission.
Photo: Amber King

When comparing fabrics, merino wool stands out as the best thermoregulator. When looking at comparative weights, it offers more insulating warmth and breathability, which equates to better thermoregulation overall. For example, the Smartwool Merino 250 1/4 Zip is the warmest and most insulating base layer in this review, packing in 250 g/m² of merino wool. The Icebreaker Oasis 200 is similar, with 200 g/m², making it a little less warm but not as thick.

Tops like the Ortovox Rock n' Wool (185 g/m²) and Carhartt Base Force Heavyweight 1/4 Zip still receive high scores but offer just a little less warmth. Both are lighter options for excellent thermoregulation on high output days like cross-country skiing or running. The Patagonia Capilene Air (147-g) is another surprisingly warm contender that does excellent work at regulating heat output. For stand-alone warmth, it's among the top contenders.

Here we test the thermoregulation of the Smartwool 1/4 Zip which...
Here we test the thermoregulation of the Smartwool 1/4 Zip which offers amazing warmth, even on this snowy day in the San Juans of Colorado.
Photo: Amber King

Through our testing, most of the polyester tops we've tested don't offer the same 'sitting around' warmth as merino wool. Many are constructed with hollow polyester fibers. When it's cold in the morning, and you pull the top on, it won't feel as cozy as merino wool simply because all the cold air is locked inside the fibers. However, once you get your body in motion, the layer will conceal the heat generated during your activity. When moving from warm to cold, tops like the Patagonia Capilene Midweight Crew and Arc'teryx Rho LT will typically adapt to their environment more readily than Merino wool. Both of these options are warmer synthetic tops than the REI Silkweight, Smartwool 150, and the Odlo Kinship Light for example, which are more breathable and not built for stand-alone warmth. Of them all, the Arc'teryx is our favorite because of the fleece liner built in that keeps the skin warm and cozy, even after we stop moving.

The first snowfall of the season. The Patagonia Capilene keeps us...
The first snowfall of the season. The Patagonia Capilene keeps us super dry and warm while on the go.
Photo: Amber King

Breathability


The yang to warmth's yin. Without great breathability, you're not going to have much warmth during your cold-weather adventures. A key metric for thermoregulation, breathability defines how well the fabric allows heat to escape in addition to how well it vents. When worn in a layered system, breathability enables fabrics to move moisture from the skin and through the fabric to the next layer, keeping your skin dry.


Choose lightweight fabric for any of the tops we reviewed if you want something that'll breathe easier. Short-sleeve options are also available, as are zip necks that offer more ventilation. If you run hot, lightweight fabric is the way to go, but if you get cold easily, opt for midweight construction.

Hiking uphill in Leavenworth, WA had us pushing the limits of...
Hiking uphill in Leavenworth, WA had us pushing the limits of breathability. One of the many ways we test our base layers.
Photo: Amber King

The best at proper ventilation are those constructed from thinner materials and a fabric knit that isn't too tight to allow moisture to escape. This is the metric where the Odlo Kinship Light really sets itself apart from the competition. The seamlessly engineered ventilation stripes through the chest and back work to increase airflow and enhance breathability by featuring a looser weave through which excess moisture can escape. This layer kept us warm enough during multi-pitch rock climbs in the fall, while also dumping enough heat to get after it on long trail runs during the shoulder seasons.

The Odlo Kinship Light getting tested on its durability limit during...
The Odlo Kinship Light getting tested on its durability limit during this multi-pitch rock climb.
Photo: Toby Swimmer

Two other tops that stand out in this metric include the Roman Trail Outfitters Merino Wool Crew and the REI Co-op Silk V-Neck. The REI Silk V-neck wicks and breathes a little better than the Roman Trail Outfitter because it's ridiculously light (only 2.4 oz) and has plenty of holes to allow ventilation through the fabric. Silk is also known for its superior wicking qualities. The Roman Outfitters is a little warmer, providing a wider range of thermoregulation, but it also vents well due to its loosely woven fabrics. We'd utilize both layers throughout the summer months but would leave the REI Co-op Silk at home during the winter. With a nicely layered system, the Roman Trail Outfitters also works well beneath a midweight fleece or jacket.

The REI Co-op Silk V-Neck offers incredible breathability that will...
The REI Co-op Silk V-Neck offers incredible breathability that will keep you dry and cool on the trail. The silk construction provides the best wicking power that you'll find out there. Here we run up a steep trail in the San Juans of Colorado on a cool day.
Photo: Amber King

The Patagonia Capilene Air Crew features a loose weave that does an impeccable job wicking and offloading moisture. This top is thicker than the above lightweight contenders, but the fibers are full of air which will keep you cool but aren't the best choice during the summer months because of the amount of insulation. However, throughout the colder seasons of the year, this layer is hard to beat due to its massive range of thermoregulation. The 100% synthetic construction of the Patagonia Midweight Capilene is also quite breathable. Its diamond-grid architecture promotes great airflow with a face fabric that cuts the wind when worn independently.

The Patagonia Capilene Air is amazingly breathable, keeping its user...
The Patagonia Capilene Air is amazingly breathable, keeping its user warm while offloading excess heat quickly.
Photo: Edward Kemper

The Smartwool Merino 250 ¼ Zip, Icebreaker Oasis, and Ortovox Rock n' Wool all offer a similar level of performance here. The Smartwool Merino 250 has a loosely knit fabric design but thicker fabrics than either the Oasis or Rock'n'Wool. The Oasis feels thinner than the Rock n' Wool but has a tighter knit construction. While these models breathe adequately for light to moderate activity, some athletes might find them too thick and warm for intense activity.

Comfort & Fit


When testing for this metric, we assess each top to determine which fabric has the coziest and most versatile fit. This is perhaps the easiest metric to test for, all we had to do was record our notes while we hung around the campfire or enjoyed a rest day. We wanted to evaluate how the fabrics felt next to our skin after several days of wear without washing, so we could determine whether or not the feel of the fabric would change over time. In general, we love merino wool tops with a fitted, stretchy design simply because it offers the maximum level of comfort.


The Smartwool 250 Zip is one of the most comfortable base layer tops in this review, followed closely behind with the Arc'teryx Rho LT due to its superb fit and fleece-lined material. The Smartwool features 250 g/m² of natural 100% New Zealand merino wool, with a bit of stretch as well as thicker cuffs and hemlines. The Carhartt Base Force Heavyweight is another with a merino wool blend that's almost as soft as the Smartwool 250 but has materials that are a touch more rigid. The Smartwool 250 has a very stretchy and long fit, while the Carhartt's shape won't deform after being worn for days on end.

The Smartwool Merino 250 is very cozy for nights at the cabin and...
The Smartwool Merino 250 is very cozy for nights at the cabin and apres ski sessions. It also moves with our bodies well when climbing pitches all day.
Photo: Toby Swimmer

The Ortovox Rock n' Wool is one of the softest merino wool options that we tested, featuring a lighter construction and 100% merino wool sourced from Tasmania, we loved how soft the wool felt next to our skin. However, we were disappointed that the latest version of the Ortovox Rock n' Wool is designed with bulkier flatlock seams across both forearms. We found these seams to be distracting and uncomfortable, they also caused bunching issues when we piled other layers over top. We hope future versions ditch the seemingly unnecessary thick seams and their placement.

We like the next-to-sin feel of the Ortovox Rock&#039;n&#039;Wool&#039;s fabric...
We like the next-to-sin feel of the Ortovox Rock'n'Wool's fabric, but we are unimpressed with the location and thickness of the seams on the forearm and chest.
Photo: Toby Swimmer

Fit

When evaluating the fit of each base layer, we handed these shirts to a group of women that varied in height, weight, and body shape to offer the most objective recommendations possible. Some were tall while others were short; some had lots of curves, while others had none. In our evaluations, tops that had a stretchier and more voluminous fit proved to be the most versatile. We also looked at the relative lengths of the arms and torso to see which provided the best overall coverage. Our lead tester (5'7", 145 lbs) prefers size Small in most of these tops but found the Kari Traa Rose, Ortovox 185 Rock 'N' Wool, Carhartt Heavyweight and Icebreaker Oasis to fit better in size Medium. We should also mention that you shouldn't be fooled by the European sizing on the Odlo Kinship Light as the snug fit allows this base layer to hold its shape and offer more ventilation during activity.

Long Arms and Torso?
Need a shirt with long arms and torso? Luckily we have a host of options. Of synthetic tops, the Arc'teryx Rho LT has super stretchy fabric that provides a next-to-the-skin fit. The Smartwool 250 1/4 Zip also has a super stretchy construction with plenty of length through the arms and torso.

Layering Ability


A good base layer is versatile and easy to use within a layering system. While most long-underwear tops are presumably the "next-to-skin" layer, it is a bonus when you can wear a tank or tee beneath when conditions are expected to warm up. Not only that, but you want to make sure you can throw layers on top and remove them without too much effort. Here, we evaluate the knit of the fabric and spend time trying on each one with different layers. Long underwear tops that do best in this category feature slippery face fabrics, a thinner construction, and thumb loops.


Synthetic layers typically have more rigid fibers that, in combination, make for easy layering. The Arc'teryx Rho LT proves to be the easiest to layer. The frictionless face fabric slides smoothly against even the fleeciest of mid-layers. We slid it over lightweight tops and under pretty much anything we wanted to layer over it. The arms are long and can be held when layering to avoid frustrating layering situations like those experienced with more friction competitors like the Smartwool 250 1/4 Zip.

The Arc&#039;teryx Rho LT easily layers over the Ortovox Rock&#039;n&#039;Wool top...
The Arc'teryx Rho LT easily layers over the Ortovox Rock'n'Wool top creating a thicker layering system to protect you from the wind. Notice the unfortunate seams of the Ortovox being visible beneath the second layer.
Photo: Toby Swimmer

The Patagonia Capilene Midweight is another great layering option with built-in thumb loops that keeps the arms in place, while the REI Co-op Midweight has frictionless face fabric and a super stretchy design that hugs your body. All are great options in this category.

One of the easiest base layers to layer over, shown here with a vest...
One of the easiest base layers to layer over, shown here with a vest and down puffy jacket for the ultimate fall weather kit.
Photo: Toby Swimmer

Of the merino wool competitors, thinner options like the Roman Trail Outfitters, Smartwool 150, Icebreaker Oasis 200, and Ortovox Rock n' Wool are much easier to layer than thicker options. Layers like the Kari Traa Rose and Odlo Kinship Light work well because of their skin-tight fit that makes sliding layers overtop easy. Of all the layers mentioned above, look for designs with longer arms so you can grab the cuff of the fabric and avoid the fabric bunching while pulling on a mid-layer.

The Smartwool 250 and the Odlo Kinship Light make a great combo for...
The Smartwool 250 and the Odlo Kinship Light make a great combo for those colder fall mornings.
Photo: Trish Matheny

Durability


The best base layers out there should last for you to receive the greatest return on your investment. A proper base layer shouldn't shrink, stretch out, pill, or fall apart after just a few months of use. Most importantly, a durable top shouldn't easily succumb to snags and tears after just a few times out on the trail. During our testing period, we shimmied through canyons and bushwhacked through forests to see if the fabric snagged or tore. We also wore each layer with loaded backpacks. After all of this, we inspect each product to evaluate the craftsmanship. In addition, we test each base layer continuously throughout the year and will update this section with our most current recommendations.


A Note on Odor
In all of our tests, the silk and synthetic shirts constructed of polyester retain more smell over time than merino wool tops. Merino wool can be worn for multiple excursions without washing before an odor becomes an issue. For this update, the Odlo Kinship Light also offers another option when it comes to fabric that doesn't retain odor. Tencel Lyocell fabric is not only soft against your skin but also features natural anti-odor properties. Despite a company's best efforts to develop odor-resistant fabrics with polyester fabrics, most will inevitably smell over time, even after washing. If you're self-conscious about a bad-smelling shirt, choose either Tencel or merino wool.

Moving uphill with a tight running pack that is fully loaded is a...
Moving uphill with a tight running pack that is fully loaded is a great way to test abrasion resistance. We love that this lightweight layer is strongly constructed with great durability all around.
Photo: Amber King

It's been seven years since we started testing the Arc'teryx Rho LT Zip, and it's still going strong. Arc'teryx is known for its bomber craftsmanship, and this product is no different. We have used and abused it while climbing, hiking, split-boarding, trail running, and canyoneering. After many long years of use, there are still no significant areas of wear and tear. Our only caveat is that the fabric retains a little smell with some pit stains in sweaty areas. Aside from that, it has truly stood the test of time and continues to meet our expectations.

With high quality construction, the Arc&#039;teryx Rho LT is one of the...
With high quality construction, the Arc'teryx Rho LT is one of the most durable layers that we've tested.
Photo: Toby Swimmer

The Patagonia Capilene Midweight is a workhorse. The synthetic fibers are strong and retain their shape, even after a few years of testing. It's no wonder it offers the best value of tops tested. The REI Co-op Midweight is also fairly durable, but the fabric is thin and pills easily after just a few washes. However, after two years of testing, it is still functional, minus some undone stitches here and there. The Carhartt Base Force Heavyweight 1/4 Zip is a top with heavy synthetic construction as well as merino wool. It proves to offer similar performance to our synthetic competitors, showing no durability issues even after heavy use and several washes.

Merino wool contenders are less durable than synthetic options, but they don't hold onto odor. Of these, the Kari Traa Rose H/Z proves to be the most durable. Unlike the Roman Outfitters Merino and Patagonia Capilene Air tops that have the least durable construction in this review, the Kari Traa Rose offers a tightly-knit face fabric that doesn't easily snag. The nylon fibers are shorter and have proven to be more durable and a better option for those needing a top for high-friction sports like canyoneering, bushwacking, or rock climbing. The Smartwool 150 is another durable hybrid that continues to perform after a year of hard use. We are constantly impressed with its performance as it has seen over 400 miles of trail use and many rock climbing adventures.

The Smartwool Merino 250 kept us warm while climbing in the shade...
The Smartwool Merino 250 kept us warm while climbing in the shade during our fall trip to Indian Creek
Photo: Toby Swimmer

Conclusion


The clothing layer next to your skin is integral for keeping you warm and comfortable while exploring the great outdoors. Whether you're snuggling up next to the fire or shredding down a double black diamond on the ski hill, aim for one that performs to meet your individual needs. We've done the hard work and tested some of the best options available. We hope that our recommendations help you select the best base layer for your next backcountry adventure.

Amber King and Trish Matheny

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GearLab is founded on the principle of honest, objective, reviews. Our experts test thousands of products each year using thoughtful test plans that bring out key performance differences between competing products. And, to assure complete independence, we buy all the products we test ourselves. No cherry-picked units sent by manufacturers. No sponsored content. No ads. Just real, honest, side-by-side testing and comparison.

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