The pajama pants bottoms have an elastic waistline with an adjustable drawstring.
At the time of our interview, Noland did not represent any of the companies we considered, but she has since gone on to represent Trew. She told us which features distinguished notable base layers in her two decades of public relations and outdoor experience.
We also picked the brain of designer Outi Pulkkinen from Duckworth to learn how fit could impact the performance of a base layer. Lastly, we talked with Robert Thomas no relation to the author of this piece , senior apparel product line manager at Smartwool, who talked to us about base-layer fit and core-spun yarn technology. The best base layer for you will be the one that fits the dimensions of your body and has a design that you are comfortable wearing.
Our female testers found the Kora Shola Crew —which we tested but was not a pick—to have a straighter, more gender-neutral fit. A good base layer also known as thermal underwear or long underwear is an article of clothing that most outdoorspeople will live in from fall until spring.
From hiking in cool and dry areas to skiing and snowshoeing to winter rock climbing, our testers played hard in these tops and bottoms in many varying climates—and then wore them some more.
For this guide, we looked at base layers that functioned as more than just underwear and worked as both a thermal layer and a wicking layer. That way you can stay warm whether you are working up a sweat, sitting around the campfire, or occupying that cold transition time in between.
Fit and comfort are the most important factors. We perused blogs and customer reviews for dozens of brands, ultimately deciding on the best model from each brand based on the reviews. To supplement what we read, we talked to dozens of outdoor-garment buyers to get their opinions on what they used in the backcountry. The inclusion of Lululemon might surprise you, but this summer we found that many John Muir Trail hikers all women were trying to stretch their dollar by using yoga wear as a base layer on the trail.
This is a phenomenon documented by REI, which featured a blog article suggesting that yoga-style pants will work for about 50 percent of people enjoying the outdoors. Because many outdoor enthusiasts look to stretch their buck by choosing activewear that works indoors, outdoors, and as a style piece, we wanted to test whether yoga wear could hold up to the standard outdoor-apparel competition. When we began picking models to test, we eliminated those made with cotton and cotton blends immediately.
While such pieces work well enough as thermals when dry and are good at wicking, cotton is not an effective insulating layer when wet either from sweat or rain. Worse yet, cotton takes so long to dry that it makes wearers feel colder than if they were wearing nothing.
Wet cotton is also more likely to cause chafing and rashes than other fabrics. By banning cotton from our review, we cut out common brands like Hanes and Fruit of the Loom the least expensive options available. We then concentrated on brands and performance fabrics meant for outdoor exercise. We also included several brands better associated with fashion or athletic wear than with the outdoors, such as Under Armour, Cuddl Duds, and Uniqlo. Under Armour has poached employees from outdoor brands and is sponsoring outdoor athletes, while also trying to take the segment from its direct competitor in the category, Nike.
Cuddl Duds, which is taking over the discount thermal arena previously held by Hanes and Fruit of the Loom, offers several models built for active pursuits. Uniqlo, a fast fashion brand, pushes its all-synthetic thermals hard during the winter and also offers discount outdoors apparel that is getting the attention of magazines like TrailGroove and Backpacker. Last year, we tested base-layer tops with all sorts of elements—hoods, half-zips, thumbholes in the cuffs, and pockets.
Some of these extras made certain base layers more desirable than the standard long-sleeve top, while an occasional poorly executed detail disqualified an otherwise great base layer. This time around, in order to arrive at the best base layer, we believed it was optimal to compare layers that were—at least superficially—designed the same way for the most part.
Another benefit of focusing on crewneck base layers is that they are more affordable than their hooded counterparts.
We also traded out midweight tops for lightweight tops this year, because last year we discovered that definitions of midweight varied more widely by company than for lightweight fabric.
Some companies, like Trew , offer only one weight. By testing lightweight layers, we were able to better determine which fabric had the best warmth-to-weight ratio versus which one was simply the heaviest. With our chosen layers in hand, our seven testers hiked, skied, snowboarded, mountaineered, and climbed their way through four months of testing.
Nearly all of our testers had thru-hiked a 2,plus-mile trail at minimum—an experience that requires living in the same base layer from four to six months—so they had opinions. They subjected a few of our top-ranked base layers to hundreds of miles of use on similar trips.
Some lived and worked in base layers, while others loved layers for casual hiking and day-to-day wear. Our testers took these base layers to extremes in Colorado, California, Oregon, Washington, Japan, and Florida why not?
Long johns keep you warm by trapping heat in the small gap between your skin and the base layer. This gap allows you to keep a relatively consistent temperature, like being in your own temp-regulated bubble, because the base layer thermoregulates, releasing warm air when the temperature rises and keeping you warm when the mercury dips.
The key is to make sure that gap is the right size. Winter-adventuring duo Justin Lichter and Shawn Forry suggested that a base layer should have a relaxed form fit—trim enough to layer over without being bulky. It should not hang off loosely from any part of your body. A tighter fit can constrict circulation, so the body feels colder. We asked testers of varying heights and body types whether the design of the layer left any body part feeling naked.
Does the fabric feel soft, stiff, or plasticky and wetsuit-like? Does it allow a full range of movement? Does it make you itch? Forry said it straight: The more minimal, the better it will feel. Some base layers up their breathability with mesh-like panels in key hot-spot areas, such as the armpits.
All the base-layer fabrics we tested were breathable, but some were more breathable than others. In addition to allowing water vapor to escape through breathable fabric, base layers help the body regulate temperature by wicking moisture drawing it away from the skin and spreading it to a broader surface area to evaporate faster. The more quickly your layer dries out, the less likely you are to feel cool and clammy while moving, or when you stop moving. Wickability depends a lot on fit.
There is nothing in the fiber that gives it that feature. They need a treatment. When a manufacturer treats these fibers on the outside of the garment with a hydrophilic or water-loving topical treatment, the synthetic fabrics start attracting water away from the skin and toward the outer layer of the fabric.
Hydrophilic treatments absorb water and disperse it to a greater surface area to reduce evaporation time. These treatments turn the synthetic fabric into a moisture-wicking layer but can wash out of the garment over time. Manufacturers can also make synthetic base layers moisture-wicking by blending hydrophilic and hydrophobic fibers, a process that tends to be more permanent. The better your layer wicks, the less cold you will feel from sweat when you stop being active.
Once moisture has wicked away from your skin and into the fabric, it should disperse across a wider surface area to help the layer dry out faster. We tested drying time by running all the layers through the wash and hanging them up. We ordered the layers based on how moist they felt right after the spin cycle. Then, every five minutes, we rearranged the order based on moistness until all the layers were dry, recording how long each layer took to attain dry status.
We did this test inside a garage, outdoors at night, and outdoors during the day, and got comparable results for each testing period. This one seems obvious, but it can be a little tricky because a base layer needs to keep you warm in a variety of temperature-changing situations.
Base layers work by switching from a wicking layer when you are active to a thermal layer when you are taking a break in the cold. They also need to work during the transition time in between. Wool has natural antibacterial features. Is the piece stylish enough to wear alone, or do you always need to wear this underwear under something else? Can it work as an athleisure or athletic-lifestyle fashion accessory in addition to a performance piece?
Noland summed up the role of style in base layers: High-end and high-price base-layer fabrics include cashmere, mohair, and alpaca wools. These materials tend to have higher tensile strengths, feel less itchy, and be less absorbent. We kept our eyes peeled for American-made long johns, as well as companies that offered recycling or take-back programs for used gear.
We also thought about ethics in the manufacturing process. People care about the treatment of the sheep raised for wool more than ever. It creates a warm microclimate, like a thin, personal temperature-regulated bubble. So the other job of a base layer—besides warming and cooling—is to wick sweat away from your skin to keep you from feeling chilled. Which fabric makes the best base layer is an age-old debate in the outdoor sphere. Wool and synthetics each have their advantages and disadvantages.
Blends aim to the capture the benefits of each one, but also have their drawbacks. The days of scratchy or itchy wool outdoor garments are gone. Base layers these days are made of soft merino wool or a Rambouillet wool both of which are named after their respective sheep breeds specifically treated for use right against the skin. Wool has much-noted antibacterial and antimicrobial properties that resist absorption of the short-chain fatty acids in sweat that cause odor.
Wool fibers are naturally stretchy, which makes the fabric feel formfitting and look flattering on a wide variety of people. Unlike synthetics, merino wool naturally wicks sweat away and breathes well after all, sheep use it to regulate their temperature, too. If a spark jumps out of your campfire, the wool layer will resist it better than the synthetic which will likely melt.
Most of our testers agreed that wool offered more warmth than synthetic options of comparable thickness and weight, which makes it perfect for less sweaty adventures like downhill skiing and snowshoeing. Generally, the finer the wool fewer microns , the more easily the yarn will bend and flex as you move, meaning it will feel less coarse and itchy. The biggest advantage of synthetic fabric over merino wool is its quick drying time.
In our drying tests, the synthetics came out of the spin cycle dry, whereas the wool and blends took almost an hour to lose moisture.
What this means for outdoor athletes is that synthetics wick more efficiently than wool—they pull sweat away, and it evaporates faster. Gram-counting backpackers may find that lightweight synthetics have an advantage over heavier wool.
Synthetic-merino blends aim to get the benefits of both fabrics while offering a high-quality base layer at a good price. Of course, these blends often also come with the negative features of their parent fabrics—odor retention, reduced insulation, and long drying times.
Our top pick, the Smartwool Merino , is constructed of an 87 percent wool and 13 percent nylon fabric made of a yarn constructed of merino wool spun around a nylon core. We reached for blends when doing endurance activities like backpacking and mountaineering because we wanted the thermal qualities of wool plus the durability of synthetic.
The Sustainable Apparel Coalition created an index to rank the environmental friendliness of various fabrics used in outdoor clothing, including base layers. It takes into account the social and labor impacts of outdoor wear, as well as the life cycle of the piece including what happens to it after it wears out. Some scientists argue that, as a natural fiber, wool is more sustainable than synthetic materials because synthetics are made of petrochemicals.
The process of manufacturing base layers—regardless of how sustainable it is—leaves an impact on the environment. The most sustainable choice you can make is finding one or a few base layers you really like and wearing them for a very long time. The SAC also tracks the ethics and labor-supply policies of outdoor-apparel companies. Brands that use wool in their base layers have been criticized for sourcing from farms with reported animal-welfare issues. Meanwhile, the relationship that outdoor-apparel companies have with their labor and suppliers is an ethical issue for both synthetics and wool, because regardless of the fabric, someone has to sew these garments.
Project Just tracks some of the brands in this guide and can give you an idea about the work conditions the sewers face based on where the garment was constructed or where the fabric was woven.
If environmental, ethical, or animal-welfare concerns influence how you shop, be sure to read up on the brands highlighted in this guide. Ultimately, the base layer you choose should have the fabric you find most comfortable. Some people are allergic to wool. Others may find synthetics scratchy. Look for a fabric that feels soft and that has a texture you like. Made from merino wool spun around a tough nylon thread core, this machine-washable and machine-dryable, odor-resistant shirt is a practical choice if you want to own only one base-layer top.
When dry, the Smartwool Merino works well as a thermal layer despite its light weight. Then I took a break in the shade at the top of the mountain in the wind, and after the surprisingly quick dry time, it was warm!
Because this shirt was thin with unobtrusive flatlock seams, it layered well in cooler temperatures without chafing us. The raglan sleeves, stitched in the same way as on a baseball shirt, prevented rubbing or chafing when we wore it with a backpack, and increased our mobility when we went rock climbing.
These tailor tricks work: Our testers found the Smartwool Merino to be flattering on the mountain as well as back at the lodge. The result is a garment that offers the benefits of wool directly against the skin, plus the strength and resilience of nylon. Our testers found base layers that used core-spun yarn to be lighter, stretchier, and softer against the skin than many of the other fabrics we tested, including the merino in the fall model.
As with any good base layer, the Smartwool Merino is meant to be formfitting, but not to cut off circulation or feel like a wetsuit. It is loose enough to allow mobility and to hide a muffin top, but tight enough to feel like a second skin under layers.
All our testers commented that the sleeves were long enough to cover their wrists well, although almost all the testers also lamented the lack of thumbholes. It was long enough to keep their torsos covered when they reached for a rock-climbing hold, with only Ibex and Under Armour offering longer shirts.
Reviewers on Amazon and the Smartwool website say that the fit of the Merino is looser than other Smartwool shirts or other models of the NTS Micro , which Smartwool has sold since I confirmed by comparing it against my almost year-old Smartwool microweight shirt: Our testers preferred the somewhat looser fit, especially compared with the skintight fit of the Duofold by Champion Brushed Back Crew.
Many of the layers we tested this year had a looser fit. The shirt is very thin. With the fall model which Smartwool does not construct with the nylon-core technology , after two months of use, the stitching on the elastic along the sleeve has become loose. Amazon reviews also voice concerns about this downfall. Several testers and other people we interviewed found the shirt to have impressive longevity: One individual hiked the entire 2,mile Pacific Crest Trail and half the 3,mile Continental Divide Trail in one microweight Smartwool shirt.
Another started seeing holes about halfway into a thru-hike of the PCT. Both testers, however, said the shirt performed so well that it was well worth the investment, even if they had to buy a new shirt when they finished. We will continue to test this top to determine its long-term durability. We were impressed that a functional, flattering design—including a reinforced neck, thick cuffs, and thumbholes—was available at such an affordable price.
What made the Cuddl Duds FlexFit crew our synthetic pick was its fit. The shirt was sufficiently long in our hands-above-head test, and the sleeves were long enough to always keep the wrist area covered, especially when we were using the much-beloved thumbholes. The cut of the neck is flattering, showing more collarbone and sternum area but not enough to make you feel cold.
In our tests, no part of the top squeezed, constricted, or hung loosely—the fit was just right, no matter the size or shape of the tester. The fabric wicked away moisture well for us, and was warm and comfortable in dry conditions. However, the amount of spandex made this base layer slower to dry than other synthetics we tested.
In our tests, multiday backpackers and those who did not wash it after a single wear complained of a smell. Because this layer is not as warm as others we tested, it is best suited for situations where you will not be outside for extended periods of time or will be in warmer, dryer conditions. Our testers enjoyed this layer for yoga, runs, or downhill skiing when they would return to warm, indoor conditions shortly after. The testers who took this Cuddl Duds top on hikes on cooler, misty days found that it did not thermoregulate as well as the competition.
It was recommended to us by low-cost hiking guru Paul Magnanti, who runs PMags. The Paradox top uses a polyester-merino blend that feels somewhere between lightweight and midweight fabric, but because the spandex is so minimal, the shirt does not have a silky sheen on the outside, which we loved.
Unlike with the Cuddl Duds top, Paradox treats this top with an oleophobic treatment a so-called odor-eliminating technology billed as Freshguard on the inside of its yarn to control odor and aid in wicking, which polyester fabrics do not naturally do. Although the treatment is supposedly embedded in the polyester fibers, our testers found that our merino wool picks still smelled better than either of the synthetic picks after a day of use.
Pierre Kim of Rhone warned us that some coated treatments in synthetics could often wash out completely after as few as 30 washes. Our testers found the zip to be an excellent addition to the basic design, especially for the price.
Multiple people we interviewed said they had owned this top for years and that it showed less wear than other base layers. Sizing tends to run about half a size larger than with the competition. It wicks away sweat while keeping you warm, all without feeling bulky.
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