Our team of experts has spent nearly a decade testing over 35 of the best base layers on the market. For 2020, we compare 9 top models for a fresh side-by-side comparison in shoulder-season and winter conditions. These tops have endured several trips across snowy mountain ridges, atop dusty desert towers, down chilly river canyons, and many nights sleeping under the stars. Each model has been put through the wringer to help you determine which product is the best choice to keep you warm and comfortable through both cold and warm seasons, no matter where you're headed.
The Best Base Layers of 2020
SmartWool Merino 250 Crew
The Smartwool Merino 250 Crew offers a thick plush material made of 100% merino wool fibers. We gave it the nickname "the Cadillac of Cush" — this top is sure to quickly become your go-to for all cold-weather activity. Outside of its superior comfort, our testers loved this top for its versatility, excellent temperature regulation, and all-natural, antimicrobial qualities. We've worn it for days on end while in the backcountry, and unlike its synthetic competitors, it was still very acceptable, stench-wise. This layer performs well in a wide range of temperatures, allowing you to quickly transition from static cold to high-exertion, all while staying warm, dry, and comfortable.
We do wish this top was slightly more durable. Through wear and washings, it began to slouch and sag a bit, but that's part of the tradeoff for the wholesome goodness of merino wool. Additionally, it is heavy when wet, and very slow to dry when the fabric becomes saturated. All in all, this layer performs beautifully in almost every situation that calls for a base layer and is comfortable and stylish enough to wear every day. If you're looking for a do-it-all layer to wear on the slopes, on river trips, and all the way to the grocery store, the SmartWool Merino 250 is tough to beat.
Read review: SmartWool Merino 250 Crew
Best Bang for the Buck
Outdoor Research Echo L/S
If you are looking for something at a more reasonable price-point, but that still qualifies as a highly technical base layer, the Outdoor Research Echo L/S checks both of those boxes. This incredibly breathable, super lightweight layer is designed for sweat-inducing activities through the warmest months of the year. Perfect for climbers, runners, or really anyone who spends much of their summertime out in the sun, the added UPF 15 treatment not only helps protect your skin, but increases the longevity of this already durable crew neck.
With a little extra fabric weight compared to others in its class, when properly layered this top will continue to keep you dry and comfortable through the winter, only adding to its value and versatility. But don't get us wrong, this is not our go-to for warmth. While we wish that the ActiveFresh odor control did a better job of keeping us smelling fresh, the Echo L/S's small pack size and quick dry time mean we're still going to bring it along on our next expedition trip, no matter the climate.
Read review: Outdoor Research Echo L/S
Best for Aerobic Activity
Patagonia Long-Sleeved Capilene Cool Lightweight
Although not the warmest of the bunch, the Patagonia Capilene Cool Lightweight is a versatile, comfortable layer that will serve you well through at least 3-seasons. This ultra-lightweight layer is at the far end of our warmth spectrum, but it was not designed to keep you cozy during the mid-winter months — unless you have a habit of running up mountains at SkiMo race paces. Instead, this layer was meant to keep you dry and moving through the other seasons, whether you are running, riding, or climbing.
As a stand-alone layer, the Capilene Cool Lightweight material hardly stands up to much more than an early-autumn chill. But this was one of our favorites for shoulder-season backpacking, and also does a great job pulling double-duty as a sun shirt. While we wished designers had left the thumb-loops in place, the silk-like feel of this layer still makes it easy to layer over, even if you occasionally lose a sleeve to the particularly grabby fleece of your favorite mid-layer.
Read review: Patagonia Long-Sleeve Capilene Cool Lightweight
Notable for Overall Performance
Patagonia Capilene Air Crew
We've never seen a base layer quite like this — well, because there's never been one. The innovative technology folded into the Capilene Air propels us into the future, and we're singing its praises. The softness and next-to-skin comfort are unparalleled; the mobility and seamless, 3D-mapped design are unbeatable; the coziness factor is rivaled only by the SmartWool Merino 250 Crew. We want to live in it, to fall in love, and grow old in it. Within a layering system, it provides enough warmth to carry you through the deepest reaches of winter, but the nearly see-through material breathes like a marathon-running monk.
Despite the high performance and versatility of this top, there are glaring flaws when it comes to justifying price and durability. It is, by far, the most expensive layer we tested. The abrasion resistance of this top is its biggest fault and is certainly not built to be dragged up chimneys and through slot canyons. The balance of cost versus durability makes this a tough top to justify, especially with other great models out there for much less money and significantly higher shelf life. We hope Patagonia improves the longevity of the Capilene Air, which would truly make it a next-level base layer.
Read review: Patagonia Capilene Air
Why You Should Trust Us
Our expert for all things comfortable and cozy is Aaron Rice. Growing up on the Atlantic coastline and living up and down the Rocky Mountains for the past decade, he knows all about making the most out of cold-weather playtime. A passion for winter weather led him to a bachelor's degree in snow and climate science — as a ski patroller in the winter you can often find him huddled in a snow pit, happily freezing his butt off to discuss the finer details of stellar dendrites. Outdoor educator and guide Roland Mott also adds experience and expertise to this review. Roland holds a degree in Outdoor Recreation Leadership and has guided rivers, backpacking, and climbing for 12 years throughout the US and Central America. He has also taught land stewardship and environmental ethics as a Master Educator for the Leave No Trace Center for Outdoor Ethics.
We identified six key metrics as essential to effectively grade a base layer top: Warmth, Breathability, Comfort/Fit, Drying Speed, Durability, and Layering Ability. Then we developed appropriate tests to carry out in the field and lab to test each metric individually. For metrics such as warmth, testing was as straightforward as wearing the garments in cold weather often and noting the relative differences. Other metrics, like durability, called for a combination of field use (i.e. chimney climbing) and lab testing (repeated dry and wash cycles and an abrasion test.) From the high desert of the US Southwest to the craggy peaks of the Pacific Northwest, we wore these tops through a variety of activities — mountain biking, climbing, uphill and downhill skiing, trail running, backpacking, and more — testing and assessing their relative strengths and weaknesses along the way.
Related: How We Tested Base Layers
Analysis and Test Results
As your go-to workhorse for sweat management, we understand the importance of having a top that will serve you well through all of your outdoor pursuits. That's why we tested the heck out of what we determined to be the best base layer tops on the market. By submitting them to everyday use, a variety of outdoor activities, and across a spectrum of temperatures and environments, we built a picture of what types of layers work best and when. We dialed-in the most important qualities and tested these layers side-by-side within these metrics to bring you the most in-depth, most helpful reviews on the internet to help you navigate purchasing the best one for your needs.
Related: Buying Advice for Base Layers
We scored each layer across our six metrics and compiled a total score out of 100 for each product. It is important to note that these scores are determined relative to the other products in the review — we purposefully chose ten of the best layers on the market, so a low score in our testing does not mean a product is not worth its mettle, it simply means it performed poorly in relation to the competition. By testing and rating each model side-by-side across these metrics, we help you to easily find the shirt(s) that score high in the categories that are significant for how you intend to use it. We describe how we tested each metric and our experiences with each layer.
The balance between price and value is always a fine line to walk when researching a product. Merino wool tops are typically more expensive than synthetic but offer benefits like superior body-temperature regulation, moisture-wicking ability, and odor resistance. Synthetic fabrics are cheaper but are sometimes not as comfortable over time. They also tend to hold onto moisture — increasing their stink-factor — and often don't provide the same warmth-to-weight when compared to their natural-fiber companions. Silk, while incredibly valuable in terms of warmth-to-weight-to-thickness, is a hard sell based on durability alone.
The argument of synthetic vs. all-natural fibers is a perpetual battle in the recreational world, and we like to think of ourselves as conscientious objectors in this fight. But for the sake of producing quality reviews based on side-by-side comparison, alas we must decide from time-to-time what materials are the best and for what situations. There are pros and cons to each material type.
This round of testing revealed the Outdoor Research Echo L/S to be the most valuable base layer on the market today. A standout for 3-season recreation and as an athletic base for the coldest months, this top is not only versatile for activities like backpacking, but performs impressively well as a technical layer on an alpine ascent. If you're value-minded, but tend to run colder, add a little warmth with an option like the REI Merino Midweight, a beefier layer that is little more reasonably priced than similarly-weighted competitors.
Warmth is one of the most important qualities when choosing your first layer. As the foundation of your layering system, the warmth of a top doesn't just lie in the thickness of the fabric or its ability to trap your body heat but in the multi-dimensional capabilities to regulate temperature. This means not only holding heat to keep you warm in colder temperatures but also allowing excess heat to escape when temps rise or your heart rate climbs. It also involves wicking away sweat from your skin to the external environment to keep you dry. All of these ingredients are essential in a product's ability to keep you warm and dry in varying temperatures and situations. A top that may be extremely warm but doesn't breathe well and holds onto moisture may work for ice fishing but will leave you dangerously wet and cold during high-output, start/stop activities like backcountry skiing.
To test the diverse range of qualities a product must exhibit to be successful in keeping you warm, we wore these layers through the varying temps of fall and winter. We brought them along with us as we skinned up windblown ridges in the Northwest, rowed through desolate canyons in the southwest, slept on frozen dirt after climbing sunny sandstone cracks in the desert, and explored trails by bike and foot in Colorado and New Mexico. Our highest scoring tops for warmth are the SmartWool Merino 250, the Patagonia Capilene Air, and Smartwool Intraknit 200. These tops consist of thicker, cushy fabrics that seal in heat while maintaining excellent breathability and wicking qualities.
What is the level of warmth for you? Depending on what you use it for, a super warm top may not be what best suits you. A really warm layer is great if you are out in extremely cold conditions, participating in activities that don't work up much of a sweat, or if you normally run on the chilly side. In this light, check out the REI Silk Crew, an impressively warm supplementary layer that doesn't add much bulk. For the deep cold of winter, we recommend the SmartWool Merino 250, our heaviest weight, 100% merino layer. What is great about this top is that it's not limited to only frigid temps. We love this top for most of the fall and spring, too, and have been happy to have it on mid-summer high altitude, windy missions, too.
If you find yourself in cool temps, participating in high aerobic activities, or want versatility across seasons - choosing a model with a lower warmth rating and a higher breathability rating may benefit you. Our Top Pick for an aerobic layer is the Patagonia Capilene Cool Lightweight, perfect for 3-season activities like backpacking or mountain biking. For cross-country and backcountry skiing, our selection of lighter weight layers like the Helly Hansen Lifa Stripe or Outdoor Research Echo L/S that still offer a bit of warmth. If you're a rock-climber anticipating long-belay stances and short bursts of energy, check out the Patagonia Air Crew or the Icebreaker 200, two tops that provide a solid level of warmth but still offer impressive breathability. It's smart to consider what temperature ranges and activities you'll be wearing your top for, and choose one that works best for your passions.
There are some specific features that we've found helped keep us warm and may help you in your search for the perfect base layer. Models like the Smartwool Merino 250, Patagonia Capilene Air, Icebreaker 200 Oasis, REI Silk Crew, Smartwool Intraknit 200, and the REI Co-op Merino Midweight have nice long arms and a drop-tail hem. These design features allow them to stay tucked into your bottoms when skiing. They also keep them from rising up and exposing your wrists, back, and belly when bending over to put on your skins or reaching for that next crimper when climbing. We found the shorter torso on the Helly Hansen Lifa Stripe leaves our bellies exposed to the biting winds when reaching overhead.
There's a lot to consider when finding the base layer that works best for you. Thinking about the temperatures and types of activities you're participating in, combined with knowledge of fabric and features will allow you to find a top that will soon become an essential part of your quiver!
Breathability is the yin to warmth's yang-- alongside warmth, it is arguably the most important quality of a quality base layer. Breathability is tied to moisture-wicking and is effectively the ability of a fabric to collect the moisture (sweat) that we all produce during activity, and move that moisture to the outside surface of the layer, where it can freely evaporate. The efficiency and speed that a fabric can convert sweat to water vapor will determine how breathable the garment is. A quality, breathable layer will help regulate your internal body temperature through wide ranges of environmental temperatures and a spectrum of energy outputs. This means it will effectively work to keep you dry and warm, or dry and cool, depending on what you need.
Breathability is an extremely important quality during active pursuits, as well as stop/start activities, like backcountry skiing. A breathable shirt will allow the moist air produced from perspiration to escape through the material and into the outside environment without saturating the fabric, thus keeping you warm and dry. A non-breathable shirt will prevent the moisture from escaping, causing it to condense on the inside of the garment. A non-breathable first layer would be miserably sweaty, wet, heavy, and therefore dangerous in cold conditions.
In addition to our assessment throughout months of use hiking, running, skiing, climbing, and biking, we also designed a test to assess each layer's breathability systematically. In a temperature-controlled, indoor environment, we worked up a sweat with the same short, rigorous exercise routine, consisting of pull-ups, push-ups, mountain climbers, burpees, and jump squats. We tested each layer side-by-side, and then timed how long it took for our skin and the inside of our shirts to dry after stopping.
The tops that earn our highest scores for breathability were also — not surprisingly — the lightest weight fabrics that didn't score highly in terms of warmth. Those were the Patagonia Capilene Cool Lightweight, Helly Hansen Lifa Stripe, and Outdoor Research Echo L/S. The Patagonia Capilene Air impressed us with its unique ability to score extremely well in both warmth and breathability ratings! The SmartWool Merino 250, Intraknit 200, and Icebreaker 200 Oasis all scored similarly in this test. All three of these layers clock in at relatively the same material weight — are we seeing a connection between weight and breathability?
Comfort and Fit
When choosing a base layer, comfort and fit are usually at the top of the list for many consumers. Even if it excels in all other categories, but fits you poorly or is uncomfortable, it won't serve you in your quest to send! This may be the toughest metric to rate because comfort and fit are ultimately subjective and different for everyone's preferences and body types. We try our best to give as subjective of an opinion as possible when considering all the factors that play into a layer's comfort and fit. We scrutinized each layer and asked the following questions: How does the fabric feel next to your skin? Is it soft, itchy, stretchy, static, warm, or cool? Does it glide against your skin or hug you like your overly-touchy Aunt Glenda?
Secondly, we considered how the garment generally fits: Is it too loose, too tight, does it constrict in particular areas — like the shoulders? How are the lengths of the torso and sleeves - does it expose your belly and wrists when reaching up? How are the cuffs? Are they too tight, do they stretch out and lose shape when worn pulled up on your forearm? Is the neck comfortable? Is it loose letting cold air draft in like a barn door, or is it too tight, and is trying to choke you out like a UFC fighter? What about mobility? Does the fabric have stretch? Are there gusseted underarms, purposeful stitching patterns, or articulated zones to help freedom of movement?
Armed with this ridiculously long, but ridiculously scrutinizing list of questions to critique each layer, we learned a lot about how a layer will perform. We're only human, and gravitated toward tops that were soft and comfortable next-to-skin. The comfiest layers are the Patagonia Capilene Air, SmartWool Merino 250, REI Co-op Merino Midweight, and the Patagonia Capilene Cool Lightweight Crew. The least comfortable against the skin is the tight-knit Merino-blend of the Smartwool Intraknit 200.
We prefer tops with sleeves that don't tend to creep up our arms, and a longer torso that avoids the always undesirable belly exposure. Slim fitting sleeves and waists, combined with well-stitched hems and cuffs tended to do the best. Tops that both fit the best and were the most comfortable are the SmartWool Merino 250, Patagonia Capilene Air, Icebreaker 200 Oasis, and the Patagonia Capilene Cool Lightweight. Performing the most poorly in this category was the Helly Hansen Lifa Stripe with an extremely short torso, resulting in belly exposure that was at an all-time high. Not far in front of that was the Smartwool Intraknit 200, whose tight-fitting arms and shoulders were in no way benefited by the stretch and engineered-articulation of the material. The REI Silk Crew, unfortunately, does not have the benefit of style, or a graceful design.
Quality of construction and thoughtful seam patterns were nice touches that increase comfort as well as mobility. We appreciated the fit of the Icebreaker 200 Oasis and the Patagonia Capilene Cool Lightweight, and the well-articulated seam pattern of the Outdoor Research Echo L/S both removed seams from the shoulders, where they often rub under the weight of a backpack, and added an extra side panel for increased movement when climbing.
A few tops were able to stand out for their superb comfort and fit while a couple left much to be desired. The Champions of Comfort are easily the SmartWool Merino 250 and the Patagonia Capilene Air both boasting soft, plush, cushy fabrics. Though on the thinner side, the Patagonia Capilene Cool Lightweight sports a magical, almost silk-like polyester. Struggling in this category is the Helly Hansen Lifa Stripe, with a tight neck that chokes us out, super short torso, and thick sleeve cuffs. Similarly, the Smartwool Intraknit 200 didn't fare well here with unusually long arms and uncomfortably narrow shoulders and tight-fitting biceps.
Durability is a characteristic that we search for in all of our outdoor gear. We spend good money on high-quality products so that we may own fewer things that will last us longer, and thus stay out of the landfill. Base layers should adhere to the same purchasing ethics that we apply (or should) to all of our consuming habits. Buy less. Buy quality. Repair when possible. When that's not possible, opt for post-consumer products — many of the polyester layers included in this review are at least some part recycled-polyester.
To test durability, we inspected the strength of the fabrics and the quality of the stitching and construction of the pieces as a whole. We also dragged them up against rocks, rolled in the dirt, plowed through manzanita and chaparral bushwacking to get to beautiful places, and subjected them to merciless amounts of washing and drying cycles. To test abrasion resistance in a controlled environment, we ground the elbows of the fabric a set number of times across a one-foot distance of gritty granite to see how the fabrics faired (think wash-board technique). This specific test gave us a very clear idea of how certain tops held up to abrasion. The Patagonia Capilene Air is the least durable top overall that we tested — think fine, open-knit cashmere sweater — but performs exceptionally in all other categories.
The broad consensus is that merino wool is, generally speaking, less durable than synthetic fabrics. Yet in our abrasion test, the thick fabric of the SmartWool Merino 250 Crew showed only surface wear. The thickness of the wool directly correlated to its durability level, but factors such as quality of materials and construction can also affect the durability of a garment. Other factors that contribute to staying-power are flatlock seams, which you will find featured on the majority of the layers in this review.
Merino wool and silk, historically, are notorious for their lack of durability, wearing holes through the fabric or shrinking/losing its shape through washes. Merino wool has come a long way in the durability that it offers — particularly considering merino-polyester blends. But when it comes to longevity, natural material still falls behind its synthetic counterparts. For a lot of folks, the performance benefits of merino wool outweigh the lack of durability, and if you take proper care of your merino top, it can serve you for a long time. Despite its reputation as being a relatively short-term fabric, several of our testers have gotten many years of use out of their merino wool tops. That said, they try to be careful to hang dry them and not wear them every single day (they are comfortable enough to want to in the winter!).
The shortest path to the grave for both merino wool and silk is through consistent washing, and particularly tumble drying of the garment. In fact, most manufacturers indicate that their wool layers are not dryer safe, and instead suggest lying the garments flat to dry. Merino wool fibers are naturally antibacterial, paired with their incredible ability to wick sweat and dry quickly. This fabric holds an uncanny power to resist body odor, whereas synthetic fabrics are infamous for quickly holding onto and even enhancing stink. This means that wool can be worn more and washed less, increasing its longevity. We suggest only washing merino layers when they are visibly dirty and disgusting, or you manage to wear them enough for them to eventually stink.
If you'll be wearing this top to scrape through slot canyons and drag yourself up rock chimneys, then durability is probably a quality you're going to want to think about. The SmartWool Merino 250 for pure merino, and either the Patagonia Capilene Cool Lightweight or the Outdoor Research Echo L/S for synthetics, are among the most durable tops we tested.
Staying dry is a foundation of being comfortable in the outdoors. Whether you need to cool down or stay warm, being wet can severely inhibit your ability to access happiness and joy. Sometimes the moisture comes from outside sources like rain or snow. Other times, it comes from a deep well of desire to work hard and push yourself, rising up to the surface as sweat. No matter where it comes from — physically or metaphorically — a top's ability to dry quickly on the body is important.
It's worth addressing that the drying speed of a fabric can differ depending on whether it is being worn or left out to dry — flat dry times and dry times on the body sometimes vary. We do expect, and often experienced a strong correlation between drying speeds when laid flat and when worn — that is, tops that dry faster on the clothesline also tend to dry faster on our bodies. The Outdoor Research Echo L/S was a perfect example of this, flat drying in as little as a half-hour, and simultaneously preventing moisture build-up on our skin, regardless of climate or body temperature level. But, of course, there are exceptions to this rule. The REI Silk Crew, with its ultra-lightweight design, had the fastest flat drying time. However, when it comes to breathability and drying out during activity, silk falls far behind rival, synthetic materials.
Our drying speed test was a simple one. We fully saturated all of the products and then laid them out to dry at the same time, then recorded the times it took for each layer to surface dry, as well as the time it took for them to dry completely. Merino wool claims that it can absorb up to 30% of its weight in moisture before feeling wet to the touch. This seemed to prove true as we had to agitate and compress the wool layers while submerged for the fibers to become saturated — a plus if you are planning to wear these layers standalone in wetter, more mild climates. The Merino wool/polyester blends of the Patagonia Capilene Air and Smartwool Intraknit 200 did a great job at resisting absorption.
An obvious observation was that thinner fabrics dried significantly faster than thicker ones — big surprise, huh?! As mentioned above, the REI Silk Crew dried lightning-fast, closely followed by the Outdoor Research Echo L/S and Patagonia Capilene Cool Lightweight. Coming in close behind with admirable dry times were the Helly Hansen Lifa Stripe as a synthetic layer, and the Icebreaker 200 Oasis, which dried quicker than the other Merino wool layers of similar weight.
The ability to layer well is an often overlooked consideration but is important for practical use in the outdoors. One of the greatest qualities of a base layer is its versatility to be worn as a single layer when you need just a little something or to be layered in a myriad of ways to keep you warm and comfortable in any temperature or situation.
To test layering ability, we thought of every way a top could be layered, and we tried all the combinations out on every garment. We observed how easy they layered as well as how they fit and felt: next to skin, over a t-shirt, over another base layer, under a sticky and tight fleece mid-layer, a sweatshirt, a puffy, a rain shell, as well as stacked in a full layering system of first (base) layer, mid-layer, puffy, and hard shell. While all layers performed well next to skin, a few did great in other areas also.
The most form-fitting layer next-to-skin is the Icebreaker 200 Oasis, and not far behind that the Outdoor Research Echo L/S. While the REI Silk Crew is awkwardly baggy, its sheer construction allows it to easily layer underneath practically anything, including heavier-weight base layers. Looser, more-relaxed fitting tops that layered well over another lightweight shirt are the Smartwool Merino 250, the Patagonia Capilene Cool Lightweight, and the REI Merino Midweight.
With such a wide array of options out there, it can be tough to narrow your search down to the layer that best suits your body type, internal temperature inclination, and intended uses. We conducted all our tests and collected our experiences into this review to try and help you choose the layer that will become your adventure sidekick for years to come! As we've stated before, it's important for you to consider the activities, temperature ranges, features, and qualities when choosing a new base layer top. We wish you luck in your honorable outdoor pursuits of fun!
— Roland Mott and Aaron Rice