SmartWool Merino 250 Crew
100% Merino Wool | Weight:
Cozy cush feel
Versatile style and doesn't stink
Heavy when wet
Not super durable
Sizing runs a bit large
We call this top the Cadillac of Cush. The Smartwool Merino 250 Crew offers a thick plush material made of 100% merino wool fibers that will immediately climb the ladder to become your beloved go-to layer. Outside of its superior comfort, it has found its way into the hearts of our testers and wins our Editors' Choice Award due to its versatility, excellent ability to regulate temperature, and stink-free factor. It performs in a wide range of temperatures allowing you to comfortably transition from static cold to high output in warmer temps, all while staying comfortable and not building up a stink.
We do wish this top was a bit more durable through wear and washings. The other downsides are that it is a bit bulky and heavy for lighter weight endeavors, heavy when wet, and slow to dry when the fabric becomes saturated. All in all this layer performs beautifully in almost every scenario that requires a base layer and is comfortable enough to wear every day. If you're looking for a comfortable do-it-all layer to follow you down the slopes, across ridge traverses, as well as to the grocery store, the SmartWool Merino 250 is tough to beat.
Read review: SmartWool Merino 250 Crew
Best Bang for the Buck
Patagonia Capilene Lightweight Crew
100% Recycled Polyester | Weight:
Doubles as a sun shirt
Not comfortable with spending triple digits to get into one? The Patagonia Capilene Lightweight Crew is a light and breathable option that offers the quality of construction and durability Patagonia is known for as well as value. Attention to detail in construction makes this a comfortable top that breathes well, dries lightning fast, and is built for movement and getting your sweat on. The impressively lightweight double knit fabric is cool, soft against your skin, and has a loose and comfortable fit. The fabric's stretch paired with its full underarm gusseted design allows for ultimate mobility while the drop-tail hem and thumb loops allow your sleeves and torso to stay in place while climbing, skiing, mountain biking, etc.
This layer proves to be a perfect balance during those even-tempered seasons, though it's not a great layer if warmth is a priority, as it is by no means made for the deep cold of winter. It excels at high output aerobic activities that require a quick-wicking, fast-drying, breathable layer. A great piece for activities like cross-country skiing, fall mountain biking, trail running, and climbing in cool to hot conditions. Light and packable, we like having the Capilene Lightweight Crew in our packs, from crag bags to carry-ons.
Read review: Patagonia Capilene Lightweight Crew
Top Pick for Breathability
Rab Merino+ 120 Crew
Merino Wool/Polyester Blend | Weight:
Fast to dry
Great temperature regulation
Great fit that layers well
Not the warmest
Not super durable
The Rab Merino+ 120 Crew quickly became a favorite among our testers with its impeccable fit, phenomenal breathability, hard-to-believe wicking efficiency, insanely fast dry time, beloved comfort, and clean look. In the field of competitors, there isn't a lightweight model that performs all-around like the Rab Merino+ 120. Combined with the inherent qualities of merino wool like excellent temperature regulation and less stink, this top is in a league of its own for active pursuits in cool to cold conditions.
This top is not a heavy hitter for low energy activities in bitter-cold conditions and being so thin; durability is not its most outstanding feature. If you're looking for a top that will perform at the highest level in active situations and breathes like the lungs of Usain Bolt, our Top Pick for Breathability will not let you down.
Read review: Rab Merino+ 120 Crew
Notable for Overall Performance
Patagonia Capilene Air Crew
51% Merino Wool, 49% Recycled Polyester | Weight:
Super cozy and comfy feel
Very low durability
We've never seen a base layer quite like this, well, because there's never been one. Patagonia's innovative technology with their new Capilene Air leaps into the future of what first layers are capable of, and we're singing their praises. The softness and next-to-skin comfort are unparalleled, the mobility and seamless design are unbeatable, and the coziness factor is rivaled only by the SmartWool Merino 250 Crew. We want to live in it, to fall and love, and grow old in it. Layered within a system, it provides warmth for the deepest reaches of winter but the nearly see-through material breathes like a marathon running monk.
The glaring thorns in the side of this high performing and versatile base layer come in the form of price and durability. It is by far the most expensive layer we tested. This top is simply not built to be dragged up chimneys and through slot canyons, its abrasion resistance is sad at best. Cost versus durability makes this a tough top to justify with other great models out there for much less money and significantly higher strength. We hope Patagonia improves the longevity of the Capilene Air which would make it next level.
Read review: Patagonia Capilene Air
We purchase every product we test for use in the field
Why You Should Trust Us
Bringing to this review a wealth of experience in a variety of outdoor pursuits is outdoor educator and guide Roland Mott. 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.
Six key metrics were identified as essential to effectively grade a baselayer top - Warmth, Breathability, Comfort/Fit, Drying Speed, Durability, and Layering Ability. For each of these, an appropriate field and lab testing protocol was developed. For metrics such as warmth, testing was as straightforward as wearing the garments in cold weather and noting 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).
Related: How We Tested Base Layers
Analysis and Test Results
A base layer, also known as long underwear, serves as the foundation of your layering system across the seasons. A stand-alone layer to regulate your body temperature through the varying temperatures of spring and fall and layered underneath insulating layers to keep you warm through the cold season, all while wicking sweat away from your body and keeping you dry and comfortable. As your go-to workhorse, 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 snot out of what we found to be the best nine layers on the market. By submitting them to the trials of use in a variety of activities and across a spectrum of temperatures and environments we nailed down what we thought were the most important qualities of long underwear shirts and tested them within these metrics to bring you the most in-depth and helpful review out there.
Related: Buying Advice for Base Layers
We scored each layer across six metrics and compiled a total score out of 100 for each product. The six metrics we tested each base layer on are as follows: Warmth, Breathability, Comfort & Fit, Drying Speed, Durability, and Layering Ability. You can view the table with the scores for each layer at the top of this screen. By testing and rating each model across these metrics, we allow you to easily find the shirt(s) that score high in the categories that are significant for how you intend to use it. Below, we describe our experience with and how we tested each metric.
A pile of warmth welcoming a fresh dusting of winter snow.
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, breathability, and odor resistance. Synthetic fabrics are cheaper but are typically not as soft next-to-skin, less breathable, and tend to hold onto stink.
Warmth is one of the most important qualities when choosing a 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 inhabit to be successful in keeping you warm we stuffed them into duffels, backpacks, and suitcases dragging them with us 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 winter hikes and mountain bike trails in the Front Range of Colorado. Our highest scoring tops for warmth are the Patagonia Capilene Air and the SmartWool Merino 250. Both of which are made of thick, cushy fabric that seals in heat while maintaining excellent breathability and wicking qualities.
Early bird gets the worm, or a summit bid all to ourselves in this case. The boys all wore different weights of merino wool baselayers on this climb up Mt. Hood.
Is 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 for you if you are out in extremely cold conditions, participating in activities that don't work up a big sweat, or tend to run on the chilly side. Tops that we'd recommend for the deep cold of winter are the SmartWool Merino 250 and the Patagonia Capilene Air
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. For cross-country and backcountry skiing or fall mountain biking a lighter weight layer that excels at breathability like the Rab Merino+ 120, Patagonia Capilene Lightweight, or the Helly Hansen Lifa Stripe may be just what you're looking for. It's smart to consider what kind of temperature range and activities you'll be wearing your top for and choose one that works best for your passions.
The Rab Merino+ 120 in its element as the king of breathability. Huffing and puffing up hills on a cool fall evening, we never overheated and it dried so fast we weren't sure if we were even sweating at all.
There are some specific features that we've found helped us keep 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, and the REI Co-op Merino Midweight have nice long arms and a drop-tail hem that allows them to stay tucked into your bottoms when skiing and keeps 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. The Patagonia Capilene Lightweight is the only top that has thumb loops which is great when we want our sleeves to stay in place to keep the cold from drafting up our sleeves. The tightly woven synthetic fabric of the Arc'teryx Phase AR did a great job with wind resistance compared to other models when worn as a stand-alone layer but didn't breathe as well when incorporated in a layering system.
Making our way down from the summit of Mt. Hood during a winter ascent. This climb is a true test of a base layer. Skinning and sweating in pre-dawn subfreezing temps for hours, then standing still on the windy summit, and finally 6,000 feet of downhill skiing.
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!
There are significant differences between a natural fiber (merino wool) and a synthetic fabric (polyester) when it comes to warmth. Key here is that they both continue to insulate when wet.
Breathability is the yin to warmth's yang and alongside warmth, arguably the most important quality in a base layer. Breathability of a garment refers to the ability of the fabric to collect moisture from the wet humid environment that you create inside your long underwear top while being active and transport that moisture from the inside of the garment to the exterior of the fabric and release it as vapor. The efficiency and speed of a fabrics conversion of liquid to vapor determine how breathable the garment is. A breathable layer will help regulate your internal body temp through diverse temperature ranges and a wide spectrum of energy output. This means it will keep you dry and warm - or - dry and cool depending on what you need.
Breathability is an extremely important quality during active pursuits and stop/start activities like backcountry skiing for example. 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.
Putting the balance of warmth and breathability to the ultimate test working up a sweat in pre-dawn below freezing temps on Mt. Hood.
In addition to our breathability assessment throughout months of use hiking, skiing, climbing, and more in the backcountry, we also designed a test to learn more about each top's capability in this category. One at a time and in a temperature-controlled, indoor environment, we worked up a sweat with the same short but rigorous exercise routine, consisting of pull-ups, push-ups, mountain climbers, burpees, and jump squats while wearing each model. We then timed how long it took for our skin and the inside of our shirts to dry after stopping.
The Patagonia Capilene Air proving its versatility, keeping us cool and comfortable in the fall Utah Sun. Its nearly see-through fabric allows for air to pass through it with ease making it extremely versatile for conditions ranging from super cold when layered, to warm weather as a stand-alone layer.
The tops that earn our highest scores for breathability were also the lightest weight fabrics and didn't score super high in warmth. Those were the Rab Merino+ 120, Patagonia Capilene Lightweight, and Helly Hansen Lifa Stripe. The Patagonia Capilene Air impressed us with its unique ability to score extremely high in both warmth and breathability ratings! The SmartWool Merino 250 was the next up with a high warmth rating and a good breathability score.
Our Award Winner for Breathability, the Rab Merino + 120 lets air pass through it like water through a colander. This feature is great for high-output activities but due to its thin merino/poly blend fabric, it isn't the warmest layer out there.
Our lowest performers in the breathability category were the Arc'teryx Phase AR and The North Face Warm. Both are made of synthetic materials, are a heavier weight and tighter weave which increases warmth but decreases their breathability. These qualities do allow them to be more wind resistant as a stand-alone layer than their more breathable friends though.
Comfort and Fit
When choosing a base layer, comfort and fit are usually the most important qualities in a person's choice. 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 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? How does the garment generally fit: Is it too loose, too tight, does it constrict through the shoulders? Torso and sleeve length - 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 too tight, does it choke you out like a UFC fighter? Mobility level: Does the fabric have stretch? Are there gusseted underarms or purposeful stitching patterns to aid in ease of movement?
Armed with this ridiculously long list of questions to critique each layer, here are some things that we found: We obviously 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 Lightweight Crew. The least comfortable against the skin is the tight-knit synthetic fabric of the Arc'teryx Phase AR.
The Patagonia Capilene Air's soft, stretchy, and airy fabric made it a favorite for comfort among the testers. It's a layer that we've found difficult to take off whether we're skiing or watching a movie at home.
We prefer tops that have a longer torso and sleeves eliminating the notorious wrist creep and the all but desirable back and belly exposure. Slim fitting sleeves and waists help with this as well. Tops that did really well with this are the SmartWool Merino 250, Patagonia Capilene Air, Rab Merino+ 120, Icebreaker 200 Oasis, and the REI Merino Midweight. Performing the most poorly in this category was the Helly Hansen Lifa Stripe with an extremely short torso belly exposure was at an all-time high.
Quality of construction and thoughtful seam patterns were nice touches that increase comfort as well as mobility. The tops that excel in this field are the Rab Merino+ 120 which fits like a custom-made Stetson and is our testers' favorite fit. As well as the Icebreaker 200 Oasis, and the Patagonia Capilene Lightweight. All tops but two incorporate offset shoulder seams for comfort while carrying a backpack. The two that have seams running across the top of the shoulders are the SmartWool Merino 250 and the Helly Hansen Lifa Stripe.
The Rab Merino+ 120 is meticulously crafted to offer a fit like a custom-made suit. A simple seam construction, drop tail hem, low profile neck, tapered sleeves, and a soft, lightweight fabric allow you to forget you are even wearing this layer.
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. We love the flawless construction and fit of the Rab Merino+ 120. The North Face Warm is the most comfortable synthetic layer we tested made with a thick and soft polyester material. Struggling in these categories are the Helly Hansen Lifa Stripe which has an awkward fit all the way through; a tight neck that chokes us out, super short torso, and thick sleeve cuffs. And the Arc'teryx Phase AR which is impeccably constructed, has a great fit, and is extremely durable but the tough synthetic material is not the most pleasant against the skin.
If possible, we always suggest trying garments on in person as it is the only way to know whether it will fit you well, and saves you the time, hassle, and the carbon impact of shipping and returning.
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 wet comes from outside sources like rain or snow. Other times it comes from a deep well of desire to work hard and push yourself in the form of sweat. No matter where it comes from, physically or metaphorically, a top's ability to dry quickly 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. With that being said, flat dry times and dry times when worn next-to-skin can vary significantly. We do expect and even experienced a strong correlation between drying speeds when laid flat and when worn. Tops that dry faster on the clothesline also tend to dry faster when worn.
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 and 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. The merino wool/polyester blend of the Rab Merino+ 120 and the Patagonia Capilene Air along with the full synthetic fabric of theArc'teryx Phase AR also did a great job at resisting absorption. The synthetic fabric of The North Face Warm happily lapped up water like a thirsty dog.
Tops during the dry speed test.
An obvious observation was that thinner fabrics dried significantly faster than thicker ones — big surprise huh?! The Patagonia Lightweight Capilene and the Rab Merino+ 120 dried lightning fast compared to all the others. Coming in close behind with admirable dry times were the Helly Hansen Lifa Stripe and the Icebreaker 200 Oasis, which dried quicker than the other merino wool layers of a similar weight. The slowest to flat dry were the two synthetic layers, the Arc'teryx Phase AR and limping into last place was The North Face Warm which took four times longer to dry than the fastest two.
Durability is a characteristic that we search for in all of our outdoor gear. We spend good money on high-quality products that 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.
To test durability, we inspected the strength of the fabrics and the quality of stitching and construction of the pieces as a whole. We also dragged them up 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 amount of times across a one-foot distance of gritty granite to see how the fabrics faired (think washing board technique). This specific test gave us a very clear idea of how certain tops held up to abrasion. The most durable top we tested is the Arc'teryx Phase AR Crew. Its tough and tight-knit synthetic fabric performs above the rest when it comes to getting dragged around and beat up. The Rab Merino+ 120 Crew and the Patagonia Capilene Air are the least durable tops overall that we tested but perform exceptionally in all other categories.
Making its way up an Eldo classic, the SmartWool Merino 250 shows off its ability to breathe and keep you comfortable in warm conditions as well as cold. The thick merino fabric makes it the most durable merino layer that we tested.
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, whereas the synthetic fabric of The North Face Warm Crew now sports a hole through the fabric. 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.
Wrestling through a vegetation-choked wash while exploring canyons, we put these base layers to the test. Not a great environment for an exposed Capilene Air.
Merino wool is notorious for its lack of durability, easily 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 but when it comes to longevity, 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. Merino wool'ss quickest way to the grave is through consistent washing and especially tumble drying of the garment. 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/disgusting, or you manage to wear them enough for them to actually stink.
The REI Co-op Merino Midweight showing its war wound after our abrasion test in the lab. This was the only 100% merino layer that developed a hole from our abrasion test.
If you'll be using your base layer 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 Arc'teryx Phase AR for synthetics and the SmartWool Merino 250 for merino are the most durable tops we tested.
The Arc'teryx Phase AR was by far the most durable top we tested. It wasn't the most comfortable next to the skin and also not as breathable as merino, but bulletproof when it came to dragging it up climbs.
Although some merino wool garments give the ok to tumble dry on low, we suggest washing on a cold cycle and laying to flat dry. This will significantly increase the longevity of your shirt.
A top's 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 layer, mid layer, puffy, and hard shell. While all layers performed well next to skin, a few did great in other areas also.
An example of a layering system. Base layer, fleece mid layer, soft shell, and down puffy. The Patagonia Capilene Air, pictured here, traps heat extremely well in a layering system but as a stand-alone layer, air cuts right thru it.
The most form-fitting layers next-to-skin are the Rab Merino+ 120 and the Icebreaker 200 Oasis. Looser fitting tops that layered well over a shirt or another base layer are the Smartwool Merino 250, the Patagonia Capilene Lightweight, and the REI Merino Midweight. The tight and tapered sleeves of the Rab Merino+ 120 Crew and the smooth face fabric and thumb loops on the Patagonia Capilene Lightweight Crew allow them to layer well underneath a tight and sticky fleece mid-layer like the Patagonia R1.
The view from the summit of Mt. Hood is more enjoyable with a solid base layer under the hood!
With such a wide array of options out there it can be tough to narrow your search down to find the base 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 that you'll most utilize in a base top. We wish you luck in your honorable outdoor pursuits of fun!