We put women's base layers to the test from Smartwool, Black Diamond, Icebreaker, Patagonia, Carhartt and more to find the warmest and most versatile options
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We've bought and tested dozens of innovative women's base layers over the last 5 years. This updated review features 17 of the market's best options, tested side by side in all kinds of conditions. Across the globe, we have sailed high seas, scaled thousand-foot cliffs, skied multiple mountain ranges, run ultra-distance miles, and camped in these performance-oriented layers. Our team assesses each product 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.
Breathable, excellent thermoregulation, extra warmth with hood, easy to layer
Super comfortable, excellent breathability, stylish, eco-conscious, no odor
Cozy fleece interior, easy to layer, warm, versatile, stash pocket, tight fit
Wide range of thermoregulation, cozy materials, no odor after long wear, longer fit through torso and arms, versatile
Stylish and functional design, excellent durability and fit, comfortable, no odor
Cons
Expensive, takes a few washes to increase next-to-skin comfort
Expensive, lacks durability of thicker fabrics, tricky to layer
More expensive, not super breathable
Stretches after wearing for several days, thick construction isn't ideal for warmer days
Expensive
Bottom Line
A top-notch lightweight performer featuring exceptional thermoregulation and breathability with an innovative Merino wool technology that gets softer with every use
A high performing lightweight base layer featuring blended Merino and recycled polyester fabrics for a wide range of thermoregulation
This high performance synthetic layer is ready for pretty much any adventure you dream up
This top provides cozy comfort, top-notch thermoregulation, and resists odor build-up better than any model we tested
This base layer offers an excellent, slim fit and a wide range of thermoregulation thanks to strategically placed ventilation panels that release excess moisture
While our testers were initially skeptical of the new Black Diamond Solution 150 Merino Hoody, we were ultimately impressed as this layer kept up with us during a variety of mountain adventures. When we first tried on the hoody, the fabric didn't feel as soft and cozy next to our skin as other layers featured in this review; however, after a few romps and washes, we noticed that it started to soften, and slowly this layer became our go-to for every mission from early morning trail runs to multi-pitch rock climbs.
This layer also grew on us thanks to the Black Diamond specific Nuyarn Merino stretch technology that wraps the merino wool fabric with a nylon core to increase strength, durability, and improve wicking capabilities. We found this layer more versatile than the rest, thanks to a hood, a 1/4 zipper, and thumbholes which can all be utilized to maximize warmth. However, we recommend sizing up if you find between sizes as this layer features a slim fit.
We've tested the Arc'teryx Rho LT Zip over many years and several iterations, 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 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 it 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. The Rho LT Zip is best for someone seeking a synthetic layer that's durable, technical, and looks great.
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 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 more length, 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.
The Patagonia Capilene Air Hoody is an excellent option for the consumer looking for style, function, and versatility. Crafted from 51% RWS-certified Merino wool and 49% recycled polyester, the unique 3D lofted knit design notably sets this layer apart from the rest. We love how the slim fit hugged our curves and kept its shape, even after multiple adventures without washing. Perhaps most notable is that the layer is incredibly versatile, functioning as more of a midweight warmth, thanks to the hood option and 3D knit weave technology, but within a lightweight layer. The Air Hoody offers an exceptional warmth-to-weight ratio when compared to the other layers in this review.
One of our only complaints with this layer is that it can be a bit of a trick to layer due to its lofted fabric and slim fit — though this certainly isn't a dealbreaker. It is also expensive when compared to other more affordable options, but we were impressed with the superior comfort, enhanced breathability, eco-conscious blend of fabrics, and exceptional warmth to weight ratio, making this our go-to for a lightweight performance layer.
This layer features a Merino wool and Capilene polyester blend that effectively increases warmth thanks to the hood and offers excellent thermoregulation due to the innovative weave design.
The Smartwool Intraknit Merino 200 really stood apart from the rest, featuring a stylish and functional design that offers gender-specific ventilation panels to enhance overall breathability and wicking capabilities. The slim fit of the 200 g/m² Merino sport yarn offers just enough stretch to increase comfort but also holds its shape even after many days out without a wash.
The Intraknit maximizes the warmth and odor neutralizing properties of Merino wool with the increased durability of polyester. Additionally, this layer is very easy to layer, as the fabric hugs the body well and maintains a smooth texture. Whether we were ascending thousands of vertical feet or out for an early morning run on the trails, it was clear to us that this high-performing base layer was our favorite crew.
Our testers love the well-engineered knit design as well as the strategically placed ventilation panels.
Credit: Steve Mace
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The Icebreaker Oasis 200 was just what we needed to stay warm, comfortable, and dry during this fall training run in Indian Creek.
Credit: Toby Swimmer
Why You Should Trust Us
Our testing team is led by Amber King and Trish Matheny. As a seasoned gear reviewer, Amber 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 the base layer tops we tested. After spending over a decade in the Tetons, Trish knows what she's looking for in base layer performance. An avid trail runner, rock climber, and splitboarder, 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.
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 and have tested them 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.
Getting high up on some granite is a great way to test the durability and thermoregulation of a performance layer.
By wearing a base layer under a wind breaker, our main tester was comfortable and cozy while trail running over 100 miles in Peru. What do you demand from a great base layer top?
Durable enough for a day of rock climbing wide cracks, this midweight layer is well-constructed and built to last.
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 and fit, layering ability, and durability.
Wondering which top offers the best performance relative to their price? We understand the importance of the 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 Trail Outfitters top is a Merino layer that retails for almost 50% less than our top performers. However, its thin materials stretches 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 synthetic 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.
The Carhartt Base Force Heavyweight is a high-value base layer top that our testers love. Its polyester-wool construction brings about the best of both worlds when it comes to materials. Comfortable, excellent breathability, with wonderful comfort. Enjoy it while hiking, running, and more.
Credit: Amber King
Warmth
How many times have you started hiking, only to start sweating and then shivering 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 will 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, 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'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.
Credit: Amber King
When comparing fabrics, Merino wool stands out as the best thermoregulator. When looking at comparable 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 Crewe is similar, with 200 g/m², making it a little less warm but not as thick. And not far behind is the Black Diamond Solution 150 Merino, which offers an exceptional range of thermoregulation within a very lightweight 150g/m² design.
Our testers love the versatility of a hood which allows the layer to trap essential heat and maximize warmth. The hood on the Solution 150 is fantastic.
Credit: Steve Mace
Tops like the Ortovox 185 Rock'N'Wool (185 g/m²) and Carhartt Base Force Heavyweight 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 Hoody and the Patagonia Capilene Air Crew (147 g/m²) are other surprisingly warm contenders that do excellent work at regulating heat output. For stand-alone warmth, they're among the top contenders.
The Capilene Air Hoody is one of our favorite base layers thanks to its innovative 3D design which offered excellent comfort and thermoregulation.
Credit: Steve Mace
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 Co-op Silkweight V-Neck or Smartwool Merino 150 Crew, for example, which are more breathable and not built for stand-alone warmth. Of them all, the Arc'teryx Rho is our favorite synthetic because of the fleece liner built in that keeps the skin warm and cozy, even after you stop moving.
The first snowfall of the season. The Patagonia Capilene Midweight keeps us super dry and warm while on the go.
Credit: Amber King
Breathability
This is the yang to warmth's yin. Without great breathability, you will not have much warmth during your cold-weather adventures. A key metric for thermoregulation, breathability defines how well the fabric allows heat to escape and 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 sometimes, as are zip necks which 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 breathability. One of the many ways we test our base layers.
Credit: Amber King
The best at proper ventilation are those constructed from thinner materials and a fabric knit that isn't too tight so moisture to escape. The Smartwool Intraknit Merino 200 is quite notable here. The stylish and strategically engineered ventilation panels throughout the design work to increase airflow and enhance breathability by featuring a tighter weave with a touch of elastane. The elastane helps to provide enough stretch to move with you during various activities. This midweight 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.
Not only does this innovative design look cool, it also offers strategically placed ventilation panels to allow the layer to breathe and release moisture.
Credit: Steve Mace
Two other tops that stand out in this metric include the Roman Trail Outfitters Merino 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 ounces) 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.
Here we run up a steep trail in the San Juans of Colorado while wearing the REI Co-op Silk V-Neck on a cool day.
Credit: Amber King
The Patagonia Capilene Air Hoody and the Patagonia Capilene Air Crew feature a loose weave that does an impeccable job wicking and offloading moisture. 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, these layers are hard to beat due to their massive range of thermoregulation. The 100% synthetic construction of the Patagonia Capilene Midweight is also quite breathable. Its diamond-grid architecture promotes great airflow with a face fabric that cuts the wind when worn independently.
The porosity of the fabric provides great airflow while you sweat your way uphill and through the backcountry.
Credit: Edward Kemper
While ascending granite rock faces for multiple pitches, our testers loved how well the Black Diamond Solution 150 Merino was able to keep us warm in the sun as well as cool in the shade. This layer features increased breathability through its Nuyarn Merino wool stretch technology and is a joy to wear. The Smartwool Merino 250 ¼ Zip, Icebreaker Oasis 200 Crewe, and Ortovox 185 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.
The Black Diamond specific Nuyarn merino wool stretch technology not only breathes well but dries faster thanks to the nylon core.
Credit: Steve Mace
Comfort and 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 have to do is record our notes while we hang around the campfire or enjoy a rest day. We also evaluate how the fabrics feel next to our skin after several days of wear without washing, so we can determine whether or not the feel of the fabric changes over time. In general, we love Merino wool tops with a fitted, stretchy design simply because they offer the maximum level of comfort.
After a few washes and some time on the trails, The Black Diamond Solution 150 Merino Hoody became one of the most comfortable base layers in this review, as is the Arc'teryx Rho LT due to its superb fit and fleece-lined material. The Black Diamond Solution features 78% Nuyarn merino wool and 22% polyester to maintain strength and durability, with a bit of stretch, as well as flatlock hemlines. The Carhartt Base Force Heavyweight is another with a Merino wool blend that has tough and more rigid materials but won't lose its shape or deform after being worn for days on end. One other great contender for superior comfort is the Patagonia Capilene Air Hoody, whose innovative and seamless 3D knit weave construction conforms to the body and eliminates chafe points to increase overall comfort.
Our testers love the slim fit of the Air Hoody which kept us comfortable while also keeping its shape during our extensive testing period.
Credit: Steve Mace
The Ortovox Rock'N'Wool is one of the softest 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 this shirt is designed with bulkier flatlock seams across both forearms. We found these seams to be distracting and uncomfortable, and they also caused bunching issues when we piled other layers over the top. We hope future versions ditch the seemingly unnecessary thick seams and their placement, because the wool itself is divine.
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.
Credit: Toby Swimmer
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 with 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 (5'6", 130 lbs) prefers size Small in most of these tops but found the Kari Traa Rose Half Zip, Black Diamond Solution 150 Merino Hoody, Carhartt Heavyweight and Icebreaker Oasis to fit better in size Medium.
Long Arms and Torso?
Need a shirt with a long torso and arms? 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 Intraknit Merino 200 also has a stretchy construction with plenty of length through the arms and extra fabric in the torso.
The length of the slim fit on the Smartwool Intraknit is slightly longer in the back than the front, offering adequate length in the torso. We love the way this top fits.
Credit: Steve Mace
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 ensure you can throw layers on top and remove them without 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 one of the easier options to layer. The frictionless face fabric slides smoothly against even the fleeciest of mid-layers, and 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. The Black Diamond Solution 150 Merino features thumbholes which help increase the ease of layering, as they hold the layer in place while putting on gloves or a midweight layer over the top.
The thumbholes help increase the ease of layering this hoody.
Credit: Steve Mace
The Patagonia Capilene Midweight is another great layering option with built-in thumb loops that keep the arms in place, while the REI Co-op Midweight Crew has frictionless face fabric and a super stretchy design that hugs your body. All are great options in this category.
This top is a little thinner than most and as a result, it's not the warmest in this review. That said, it does well as a base layer in colder weather and is easy to layer.
Credit: Amber King
Of the Merino wool competitors, thinner options like the Roman Trail Outfitters, Smartwool 150 Crew, Icebreaker Oasis 200, and Ortovox Rock'N'Wool are much easier to layer than thicker options. Layers like the Kari Traa Rose and the Smartwool Intraknit Merino 200 work well because of their skin-tight fit, making 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.
When the sun goes down and it's time to layer up, you'll have no problem layering over this smooth fabric.
The Kari Traa Rose is stylish and a great layering piece.
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 a loaded backpack. 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 odor becomes an issue. 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 great way to test abrasion resistance. We love that the lightweight Smartwool 150 Crew is strongly constructed with great durability all around.
Credit: Amber King
It's been many years since we first 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, and we have some pit stains. Aside from that, it has truly stood the test of time and continues to meet our expectations.
With high quality construction, the Arc'teryx Rho LT is one of the most durable layers that we've tested.
Credit: 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 some of 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 is a top with heavy synthetic construction and Merino wool. It offers similar performance to our synthetic competitors, showing no durability issues even after heavy use and several washes.
The Capilene Midweight Crew features exceptional breathability and a fast drying speed, wrapped into a lightweight and durable product. It'll last you for many years with a low overhead cost.
Credit: Amber King
Merino wool contenders are less durable than synthetic options, but they don't hold onto odor. Of these, the Kari Traa Rose Half Zip and the Smartwool Merino 250 prove to be the most durable. The Kari Traa has 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.
This versatile layer performed well in nearly every metric.
Credit: Steve Mace
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 our recommendations help you select the best base layer for your next backcountry adventure.
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.
