Our Editors independently research, test, and rate the best products. We only make money if you purchase a product through our links, and we never accept free products from manufacturers. Learn more
We've bought and tested dozens of innovative women's base layers over the last 5 years. This updated review features 19 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.
Editor's Note: This review was updated on November 15, 2022, to include new offerings from Patagonia and Ridge Merino, as well as the latest versions of long-standing favorites from Arc'teryx and REI Co-Op.
While our testers were initially skeptical of the Black Diamond Solution 150 Merino Quarter Zip, 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 and 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're in-between sizes, as this layer features a slim fit.
We've tested the Arc'teryx Rho LT Zip Neck 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 both over and under, plus the zippered neck for optional ventilation. This is 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, wear and tear are minimal, even after 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 also 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.
The Ridge Merino Aspect Midweight is a high-performing Merino wool base layer whose features far exceed the modest price tag. Constructed with 84% Merino wool and 16% nylon, it is one of the softest base layers that we've tested, while the nylon increases both durability and structure. Naturally odor-free, this layer can be worn for weeks between washes, and the thoughtfully placed flatlock seams increase comfort and prevent chafing when shouldering a heavy backpack.
While we do not consider this a midweight as advertised, it is an exceptional lightweight garment that is easy to layer over the top of. The slim-fitting, versatile design effectively traps body heat when temperatures drop and dumps excess heat when you pick up the pace. While not the warmest layer that we've tested, this is a great choice for the base of your cold-weather layering system.
The REI Co-op Midweight Base Layer Crew is a great choice for those seeking a highly functional synthetic base layer with an affordable price tag. This garment offers enough warmth for those in-between-season days and is available for a fraction of the cost of its top-performing synthetic competitors. It also has durable features such as flatlock seams and thumb loops that give us confidence this layer will be around for many seasons to come.
We were disappointed by the synthetic polyester blended fabric, as we noticed it retained odor almost immediately. And while the fabric successfully wicked moisture and sweat away from our skin, this layer couldn't efficiently release moisture through the tightly woven fabric, so it took longer to dry. This sometimes would mean sacrificing precious warmth during colder temps, so we do not recommend this layer for high output activities nor for the depths of winter. Overall, our testers were happy with the slim-fitting, durable design that kept us warm during the shoulder seasons or as the base of our layering system for moderately cold weather adventures.
The Patagonia Capilene Thermal Weight Zip-Neck quickly stood apart from the competition in terms of warmth and breathability. Our lead tester loves this layer as a stand-alone piece for efficiently shedding sweat accumulated on fall trail runs as well as the base of her cold weather kit while rock climbing during those crisp October nights. While not a thermal weight as advertised, the polyester blended fabric and micro-grid fleece interior gave a memorable performance in terms of exceptional breathability and moisture-wicking capabilities.
Patagonia advertises a Polygiene odor control treatment for the Capilene Thermal, but we found this layer to retain body odor almost immediately, especially when used several days in a row. And while we appreciate the thumb loops in terms of layering ability, the low-quality construction (basically just an elastic band) doesn't inspire confidence they will last for the life of the base layer. That said, this layer offers excellent thermoregulation and breathability thanks to the air-permeable Polartec fabric and the long zip neck. These work together to effectively dump heat and excess sweat during those high-intensity mountain pursuits.
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.
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. 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. 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.
Our women's base layer testing is divided across five rating metrics:
Warmth (25% of total score weighting)
Breathability (25% weighting)
Comfort and Fit (20% weighting)
Layering Ability (20% weighting)
Durability (10% weighting)
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.
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 tops offer 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 Merino Long Sleeve retails for less than half many of our top performers. However, its thin materials stretch out over time, and you end up sacrificing durability.
A couple of our favorite value-based purchases of all the garments that we've tested are the Ridge Merino Aspect Midweight and the REI Midweight Base Layer Crew. The Ridge Merino is on point with some of our top-performing base layers, while the REI Midweight offers incredible value in exchange for sufficient synthetic performance. However, it's also worth considering the long-term value of synthetic tops like the Arc'teryx Rho LT. Its superior craftsmanship and high quality make it one of our top choices season after season of use, which reduces its total cost over time.
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, plus one silkweight. 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.
When comparing fabrics, Merino wool stands out — it offers more insulating warmth and breathability, which equates to better thermoregulation overall. For example, the Smartwool Classic Thermal Merino 1/4 Zip is among the warmest and most insulating base layers in this review, packing in 250 g/m² of Merino wool. The Icebreaker Merino 200 Oasis 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.
Tops like the Ortovox 185 Rock'N'Wool (185 g/m²) and the 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.
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 Silk V-Neck or Smartwool Classic All-Season Merino, 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 built-in fleece liner that keeps the skin warm and cozy even after you stop moving.
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.
At the top of this metric was, surprisingly, the Patagonia Capilene Thermal Weight Zip-Neck. Our testers were blown away by the wicking capabilities and fast drying times of this impressive layer. Though not the advertised thermal weight, in our opinion, it offers exceptional breathability and warmth thanks to its micro-grid fleece interior. Keep in mind, while not a true thermal weight, this is still a layer better suited to cool temps.
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.
Essentially, the layers that excel at proper ventilation are those constructed from thinner materials and a fabric knit that isn't too tight for moisture to escape. The Smartwool Intraknit Thermal Merino 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.
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 Crew is also quite breathable. Its diamond-grid architecture promotes great airflow with a face fabric that cuts the wind when worn independently.
When spending long days rock climbing, 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.
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 Hoody became one of the most comfortable base layers in this review. The Arc'teryx Rho LT is also notable thanks 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. 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.
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.
Another super soft Merino wool option that stood out amongst the competition is the Ridge Merino Aspect Midweight. It features a very basic crew construction with strategically placed flatlock seams that reduce bulk and prevent chafing while carrying a heavy pack. Our testers love the long cut and slim fit that effectively trapped our body heat, as well as the discreet yet functional thumb loops that added warmth and structure to the overall design.
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 Arcteryx Rho LT, Black Diamond Solution 150, and the Kari Traa Rose Light Half Zip 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 Patagonia Capilene Thermal Weight Zip-Neck and the REI Co-op Midweight both have super stretchy fabric that provides a next-to-the-skin fit. The Smartwool Intraknit Thermal and the Ridge Merino Aspect also feature a stretchy construction with plenty of length through the arms and extra fabric in the torso.
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 — 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 Patagonia Capilene Midweight and the Patagonia Capilene Thermal Weight Zip-Neck are both great layering options with built-in thumb loops that keep the arms in place, while the REI Co-op Midweight features thumb loops and a frictionless face fabric in addition to a super stretchy design that hugs the body. All are great options in this category.
Of the Merino wool competitors, thinner options like the Roman Trail Outfitters, Smartwool Classic All-Season Merino, and Ridge Merino Aspect are much easier to layer than thicker options. Layers like the Kari Traa Rose and the Smartwool Intraknit Thermal work well too because of how fitted they are, making sliding layers over them easy.
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.
It's been many years since we first started testing the Arc'teryx Rho LT Zip, and prior versions are 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, and we expect the same to be true of the most current version. Our only caveat is that the fabric retains a little smell. Aside from that, it has truly stood the test of time and continues to meet our expectations.
The Patagonia Capilene Midweight is a workhorse. The synthetic fibers are strong and retain their shape, even being put throught the wringer. Another favorite in this metric is the Patagonia Capilene Thermal Weight Zip-Neck thanks to its stretchy and durable polyester blended outer and soft microgrid fleece interior. Our only complaint is that the thumb loops lack the same quality as the rest of the layer — they are thin and don't inspire long-lasting confidence. The REI Co-op Midweight is also fairly durable, featuring reinforced flatlock seams and thick thumb loops.
Merino wool contenders are less durable than synthetic options, but they don't hold onto odor. Of these, the Kari Traa Rose Half Zip is the most durable. It 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, bushwhacking, or rock climbing.
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.
Looking for the best women's winter jacket? We've...
Ad-free. Influence-free. Powered by Testing.
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.