For nearly a decade, our team of experts have tested over 35 of the best base layers on the market. For this update, we compare 11 top models to bring you a comprehensive review of the latest and best options available. From ski slopes to backpacking trips, down chilly river canyons, and through many nights sleeping under the stars, our team put these layers through the wringer. By comparing each model side by side, we're able to help you decide which model is the best option to keep you dry and comfortable through both the warm and cold seasons, no matter where your next adventure takes you.Related: Best Base Layer for Women
Best Base Layer for Men
|Price||$52.25 at Backcountry|
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|$129.00 at Backcountry||$59.99 at Amazon||$71.25 at Backcountry|
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|Pros||Temperature regulation, ultra-cozy, balance of warmth and breathability||Lightweight, insanely comfy, warm, breathable, versatile||Affordable, fashionable fit, breathable||Comfortable, nice fit, breathable, versatile, quick to dry, odor resistant||Heavier and warmer than most midweight tops, thumb loops, long cut|
|Cons||Expensive, recommend special laundering, slow to air-dry||Super expensive, extremely poor durability||Finer thread Merino is not quite as warm, slightly itchy, shoulder top seams||Expensive, lack of durability, heavy when wet||Slow to dry when saturated, questionable durability|
|Bottom Line||This top is the gold standard for staying warm, dry, and comfortable during and after all of our outdoor adventures||Implementing new and innovative technology, Patagonia brings us a seamless base layer that feels unbelievable||A fine Merino base layer at an entry-level pricepoint||This doesn’t stand out among the crowd, but silently gets the work done without a need for recognition||Thoughtful features like thumb loops and an extra long cut will surely help add a little extra warmth to your winter|
|Rating Categories||SmartWool Merino 250 Crew||Patagonia Capilene Air Crew||Meriwool Midweight Thermal||Icebreaker 200 Oasis||Ridge Merino Inversion Crew|
|Comfort And Fit (20%)|
|Drying Speed (10%)|
|Layering Ability (10%)|
|Specs||SmartWool Merino...||Patagonia Capilene...||Meriwool Midweight...||Icebreaker 200 Oasis||Ridge Merino...|
|Material||100% merino wool||51% merino wool/49% recycled polyester||100% merino wool||100% merino wool||100% merino wool|
|Fabric Weight||250 g/m²||190 g/m²||250g/m²||200 g/m²||270 g/m²|
|Weight (size M)||9.3 oz||6.6 oz||9.8 oz||7.7 oz||11.0 oz|
|Types available||crew, 1/4 zip, hoody||crew, hoody||crew||crew, short sleeve, half zip||crew|
|Air Dry Test (minutes)||50||40||45||35||70|
|Fit||Slim fit||Slim fit||Slim fit||Slim fit||Slim fit|
|Stitching||Flatlock seams||Seamless 3D construction||Flatlock and flat seams||Flatlock seams||Flatlock and flat seams|
|Shoulder top seams?||No||No||Yes||No||No|
|Drop tail hem?||No||No||Yes||Yes||No, but extra long cut|
SmartWool Merino 250 Crew
A top that is likely to earn its place as your go-to for all cold weather activity, the SmartWool Merino 250 Crew continues to shine in this category. Not only does this top offer superior comfort next-to-skin, but it is remarkably versatile as a mid-layer. You can lean on the 100% merino wool weave for its excellent temperature regulation, moisture wicking capability, and all-natural antimicrobial qualities. We've worn it for days on end, both at home and out on multi-day backcountry trips. Unlike its synthetic competitors, it somehow manages to be very acceptable, stench-wise, after multipe wears between washes. 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.
As to be expected of natural fibers, this top will begin to slouch and sag a bit through consistent wear. And as is true of all merino tops we tested, including the Merino 250 Crew, special care with washing and drying should be taken to ensure the longevity of this layer. When the fabric becomes saturated—as with handwashing—this base layer is comparatively slow to dry. While we do wish for increased durability, considering the thick fabric weave this top performed surprisingly well in our abrasion test, only accruing surface scarring. From the crag to the mountain and then back down for a night on the town, the SmartWool Merino 250 is comfortable and stylish enough to wear every day, for practically every activity.
Read review: SmartWool Merino 250 Crew
Best Bang for Your Buck—Merino Wool
Meriwool Midweight Thermal
You may be surprised to discover that you actually don't have to pay an arm and a leg for a superb merino wool top. The Meriwool Midweight Thermal offers near top-quality performance at a fraction of the cost of most of the 100% Merino tops we tested. Even though it is firmly in the midweight category, we found that the extra-fine spun wool used to create this layer is more breathable than other directly comparable models, making it a great option for folks engaged in high-output activities like ski touring. Couple that with a slim, stylish fit, and you have a layer you can take from the mountain straight to après-ski.
The benefits of increased breathability do come at the sacrifice of a bit of warmth — so don't expect this layer to be quite as warm as other 250 g/m² options included in this review. Though soft, the Merino wool is slightly itchy at first and takes some breaking in (read: responsible washing and drying) before it is snuggly-comfy. We hope that designers opt to move the seams off the shoulder top with future updates, which can rub when wearing a heavy pack. Beyond these small critiques, the Meriwool Midweight Thermal presents a reasonable entry-point into all-natural base layers.
Read review: Meriwool Midweight Thermal
Best Bang for Your Buck—Synthetic
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 also 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
While it may not be the warmest of the bunch, the Patagonia Capilene Cool Lightweight is a versatile, comfortable layer that is able to serve you well through most of Spring, Summer, and Fall. 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 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 (as previous models included), the silk-like feel of this layer still makes it easy to layer over to add some warmth as needed. If you need long sleeves for aerobic activities, this top from Patagonia is our strong recommendation.
Read review: Patagonia Long-Sleeve Capilene Cool Lightweight
Notable for Strong 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 Patagonia 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 incredibly well, too.
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. It is certainly not built to be dragged up rock chimneys and through slot canyons. The balance of cost versus reliability makes this a tough top to justify, especially with other great, more durable models out there for much less money. We hope Patagonia is able to improve the durability of the Capilene Air, which would make it a next-level 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 bushwhacking) and lab testing (repeated dry and wash cycles and an abrasion test.) From the high desert of the US Southwest to the craggy peaks of the Pacific Northwest, we wore these tops through a variety of activities—mountain biking, climbing, uphill and downhill skiing, trail running, backpacking, and more—testing and assessing their relative strengths and weaknesses along the way.
Related: How We Tested Base Layers
Analysis and Test Results
As a workhorse for thermoregulation, we understand the importance of having a base layer that will serve you well through all of your outdoor pursuits. That's why we started with only the best models tops on the market and then proceeded to field test the heck out of them. By submitting them to the wear-and-tear of everyday use and a variety of outdoor activities across a spectrum of temperatures and environments, we are best able to dial-in which types of layers work best in what situations. We targeted the most important qualities to analyze, and tested these layers side-by-side according to these metrics. We offer this comprehensive review to help you land on the best base layer for your own needs.
Related: Buying Advice for Base Layers
It is important to note that the assigned scores are determined relative to the other products in the review. We purposefully chose to test the best layers on the market, so a low score in our testing does not mean a product is not worth its mettle. It simply means it performed poorly in relation to the competition. We understand that the individual metrics that are important to some may not be as important to others. By testing and rating each of these layers relative to one another, we are able to highlight which score highest in the metrics that are significant for how you intend to use it. Our ratings are based on specific tests we perform and backed up by personal experience while using each of these products extensively in the field.
The balance between price and value is a fine line to walk when researching a product. The argument of synthetic vs. all-natural fibers is a perpetual battle in the recreational apparel world, and we like to think of ourselves as conscientious objectors in this fight. But for the sake of producing quality reviews, alas, we must decide from time to time what materials are the best for certain situations. There are certainly pros and cons to each material type.
Synthetic fabrics tend to be less expensive, a touch more durable, and pack down smaller. They also tend to hold onto moisture, retain odors over time, and often don't provide the same warmth-to-weight when compared to their natural-fiber companions. Merino wool tops are typically more expensive and bulkier, but offer benefits like superior body-temperature regulation, moisture-wicking ability, and odor resistance. Silk, while incredibly valuable in terms of warmth-to-weight-to-thickness, is a hard sell based on durability alone.
The Outdoor Research Echo L/S is one of the most valuable synthetic layers 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. If you're value-minded but tend to run colder, add a little warmth with an all-natural option like the Meriwool Thermal Midweight, a 100% merino wool layer that is very reasonably priced compared to its direct competition.
As the foundation of your layering system, warmth is one of the most important qualities to consider in your decision. It is not just about simple heat retention, but rather the complex system of thermoregulation. A good base layer should trap heat to keep you warm in cold temperatures and also allow excess heat to escape when your heart rate climbs and body temperatures rise. It also involves wicking away sweat to keep you dry and protected from evaporative cooling. All of these ingredients are essential to a layer's ability to keep you warm and dry through a range of temperatures. An intensely warm top that doesn't breathe well may work for ice fishing, but it will likely leave you dangerously wet and cold during high-output activities like backcountry skiing.
We wore these layers through the varying temperatures of fall and winter to test every quality that results in you successfully staying warm and dry. We wore them as we skinned up windblown ridges in the Northwest, rowed through desolate canyons in the Southwest, slept on the frozen dirt after climbing sunny sandstone cracks, and explored trails by bike and foot in Colorado and New Mexico. The standout tops for well-balanced warmth are the SmartWool Merino 250, the Patagonia Capilene Air, and Ridge Merino Inversion. These tops consist of thicker, cushy fabrics that seal in heat while maintaining excellent breathability and moisture-wicking abilities.
For those who work in extremely cold conditions or normally run on the chilly side, you may want to seek out those tops that favor pure warmth over breathability. The REI Silk Crew is an impressively warm, surprisingly thin layer that can supplement winter-wear without adding much bulk. For the deep cold of winter, we recommend the Ridge Merino Inversion, our heaviest weight, 100% merino layer. This top is designed specifically with snow sports in mind, incorporating features like thumb-loops and an extra-long hem, both which help minimize skin exposure to cold air.
If you are looking for a layer that better suits highly aerobic activities, or you want versatility across seasons, you will likely benefit from choosing a lighter weight layer that prioritizes breathability over warmth. Our testers' favorite for an aerobic layer is the Patagonia Capilene Cool Lightweight — this top is perfect for 3-season activities like backpacking or mountain biking. For cross-country and backcountry skiing, we would opt for lightweight layers that still offer a bit of warmth, like the Helly Hansen Lifa Stripe or Outdoor Research Echo L/S. If you're a rock-climber anticipating long-belay stances and short bursts of energy, check out the Patagonia Air Crew, Icebreaker 200, or SmartWool Merino 250, which all provide a solid level of warmth but still offer impressive breathability.
There are some specific features that we've found help keep us warm and may help you narrow your search for the perfect base layer. Models like the Icebreaker 200 Oasis, Smartwool Intraknit 200, and the REI Co-op Merino Midweight have nice long arms and a drop-tail hem. Like the extended-cut of the Ridge Merino Inversion, this design feature helps 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 climbing skins or reaching for that next crimper when climbing.
Breathability is the yin to warmth's yang. Alongside warmth, it is arguably the most important quality of an effective base layer. Breathability is tied mainly to the moisture-wicking capability of a fabric. Effectively, this is the ability to collect moisture (sweat) and move that moisture to the outside surface of the fabric, where it can freely evaporate. The breathability of a garment is determined by how quickly and efficiently a fabric can convert sweat to free water vapor. A quality, breathable layer will help regulate your body temperature through a range of environments, regardless of your energy output. Depending on the situation, a great base layer will effectively work to keep you dry and warm, or dry and cool, depending on how it's designed.
Breathability is an extremely important quality during active pursuits, as well as stop/start activities like backcountry skiing or rock climbing. A breathable shirt will allow the moist air hovering over your skin to escape through the material without saturating the fabric, thus keeping you warm and dry. A non-breathable shirt will prevent that moisture from escaping, leading it to condense on the inside of the garment. This leaves you wearing a sweat-saturated shirt that is wet, heavy, and potentially dangerous in cold conditions.
We assessed each layer's breathability systematically to back up our findings after months of use hiking, running, skiing, climbing, and biking. We tested each layer side-by-side in a temperature-controlled, indoor environment. We used the same short, rigorous exercise routine to work up a sweat, and then after stopping, timed how long it took for our skin and the inside of our shirts to dry.
Not surprisingly, the tops that earn our highest scores for breathability are also the lightest weight fabrics that incidentally didn't score as well in the warmth metric. Those are the Patagonia Capilene Cool Lightweight, Helly Hansen Lifa Stripe, and Outdoor Research Echo L/S. As a bit of an outlier, the Patagonia Capilene Air, continues to impress with its unique ability to balance warmth and breathability masterfully. The Meriwool Midweight Thermal, Intraknit 200, and Icebreaker 200 Oasis proved the most breathable of the Merino layers, and all scored similarly in this test. You also might notice that these three layers tip the scales at relatively the same material weight — for Merino tops, there is a clear 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 cling too tightly?
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? 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 long but scrutinizing list of questions to critique each layer, we learned a lot about how a layer will perform. We're only human; we 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, Ridge Merino Inversion, 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. The tops that really do a great job of balancing fit and comfort are the SmartWool Merino 250, Patagonia Capilene Air, Icebreaker 200 Oasis, and the Patagonia Capilene Cool Lightweight — the Ridge Merino Inversion also falls into this category, and is the only base layer we tested that incorporates thumb loops. Performing the most poorly in this category was the Helly Hansen Lifa Stripe with an extremely short torso, resulting in belly exposure 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 upper body mobility.
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, Patagonia Capilene Air, and Ridge Merino Inversion, all 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, uncomfortably narrow shoulders, and tight-fitting biceps.
Durability is a characteristic that we search for in all of our outdoor gear. We often spend on high-quality products to 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 limiting washing merino layers when they are visibly dirty, or you manage to wear them enough for them to stink eventually.
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 stand-alone 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 merino wool Icebreaker 200 Oasis, which dried quicker than the other wool layers of similar weight. The Ridge Merino Inversion, with the thickest fabric weight of any Merino layer we tested, came in last in this category.
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 layer underneath practically anything easily, 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. 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