Best Base Layers (2026): Merino Wool, Synthetic, and More (original) (raw)

The Best Base Layers for Every Adventure

Whether you’re layering up for winter cold or looking for an ultralight summer system, I’ve tested and found the best base layers for all your outdoor adventures.

Featured in this article

The Best Ultralight Merino Wool Base Layer

Ibex Woolies Pro Tech Crew

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Best Midweight Base Layer

Icebreaker Merino 200 Oasis Thermal Top

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The Best Heavyweight Base Layer

SmartWool Classic Thermal Merino Base Layer

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The Best Base Layer for Extreme Cold

Minus33 Heavyweight Yukon Thermal Long Sleeve

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Base layers, thermal underwear, long johns—whatever you want to call them, nothing in the process of layering clothing for warmth is as important as the layer that touches your skin. This layer has to do double duty, insulating you but also allowing heat and moisture to pass through it and out, away from your body.

To find the best base layers for different scenarios, I've spent years testing them while hiking alpine lakes in the summer, snowshoeing through the winter, and making dozens of trips between those extremes. These are my favorites.

Be sure to also check out WIRED’s guides to the Best Merino Wool, Best Rain Jackets, Best Daypacks, Best Backpacking Tents, and all the rest of WIRED's outdoor coverage.

Updated March 2026: We added the Ridge Merino balaclava, Carhartt's Base Force, and some more notes on how to choose the best base layer. We also updated links and prices.

• The Best Ultralight Merino Wool Base Layer

Ibex

Woolies Pro Tech Crew

Ibex Woolies Pro Tech Crew and matching Woolies Pro Tech Bottoms ($115) are the best lightweight merino base layer I've tested. They've been the top pick in our merino wool clothing guide for years, and I struggle to imagine what would unseat them.
Woolies are Nuyarn, which is 85 percent merino wool and 15 percent nylon. The merino wool is wrapped around a nylon core, which increases the warmth while being lighter (5 ounces for the men's large) and more durable. Woolies are 125-gsm wool (that's grams per square meter, a common measurement of fabric thread density, and therefore relative warmth). The cut here is next-to-skin tight, which is part of what I like about the Woolies—it's easy to get your next layers over them, and they don't bunch up. There are generous thumb holes on the sleeves which make it easy to pull on additional layers without the sleeve riding up. The flatlock stitching makes it so I don't notice the seams (which are mostly off the shoulder anyway, to prevent any rubbing should you be wearing a pack).
I've been wearing Woolies as my main base layer in winter for four years now. This is also my top pick for all things technical—backpacking, bike packing, climbing, skiing, etc. It's what I bring hiking and backpacking to elevation in the summer months as well. Paired with a merino grid fleece and lightweight puffer jacket, this is even enough for shoulder-season trips in the fall. I prefer the crew T-shirt since I usually have other things over this anyway, but there is a quarter zip version of the shirt if you prefer to have more ventilation options. If these have a con, it's that they frequently sell out in popular size and color combos. (They also restock frequently, so keep checking if the one you want is not currently available.)

• Best Midweight Base Layer

  • Photograph: Scott Gilbertson
    Icebreaker

Merino 200 Oasis Thermal Top

Icebreaker's 200 Oasis base layer is, as the name suggests, a 200-gsm base layer, making it a good choice for a wide variety of uses, whether its skiing in the front country, hiking in the fall or spring, or as part of your layering system in the depths of winter. The 100 percent merino fibers here are not quite as soft at the Smartwool above, but they're equally good at regulating body temperature and wicking away moisture. This is also the fastest drying of the merino tops I tested.
The flatlock stitching, combined with offset shoulder seams, make this one plenty comfortable. The gusseted underarms are nice for increased mobility. My one gripe with this is that I feel like it could be longer. Sometimes when I lift my arms over my head this one rides up quite a bit, exposing my stomach. For that reason I would not recommend this if you're on the taller side, or have long arms (for reference, I am 5'11" and wear a large).

• The Best Heavyweight Base Layer

  • Photograph: Scott Gilbertson
    SmartWool

Classic Thermal Merino Base Layer

Smartwool's 100 percent merino Classic Thermal base layer is another staple from our years of merino wool coverage. It's 250-gsm merino, double the thickness of the Ibex Woolies, and roughly twice as warm, making it a great base layer for cold weather. It fits looser too, making it feel more like a comfortable shirt. The looser fit makes it possible to use this as a second base layer over something like the Woolies when it's extremely cold (this combo is something I wear all the time here in Northern Wisconsin). Part of the reason I love this top especially is that it's soft and comfortable, keeping you warm without that tight, “technical garment” feeling. It also manages to not feel too bulky when you add a midlayer over it. Be sure to grab the bottoms as well.
The 100 percent merino means the Classic Thermal effectively wicks moisture, keeping you warm even if you get wet with sweat. Merino also means it won't stink. As with many of the tops on this page, the flat stitching and off-the shoulder seams mean you won't get any rubbing while wearing this with a pack. If I had to come up with a downside, it'd be that this is really warm and might be overkill if you live in, say, Southern California. For the rest of us though, this is a great all-around option that works well on the trail or just sitting around the house on those dark winter evenings.

• The Best Base Layer for Extreme Cold

  • Photograph: Scott Gilbertson
    Minus33

Heavyweight Yukon Thermal Long Sleeve

If you're going to be in serious cold, New Hampshire–based Minus33 is the company to shop. Where I live, winter temps regularly dip below 0 degrees Fahrenheit and the Yukon comes into its own. The 400-gsm weave of 100 percent merino is more like a sweatshirt than a base layer, but if you live in the north, you get it. To be honest, I usually go with the Woolie crew under this on really cold days, especially for low-aerobic activities like walking the dog before the sun is up. For most people, the Yukon (or the Tanana, as the women's version is called) is probably overkill, but if you live in the north, or if you're a perpetually cold person, this is the ultimate heavyweight base layer.
The Yukon is wonderfully soft on the inside, and the seams don't rub, even with a heavy pack on. The cut is roomy without being too baggy, and it's machine-wash and -dry, so no babying necessary. I've been wearing this shirt in winters for several years now, and it still looks pretty much like it did the day I got it—almost no pilling and no fraying.

• Best Value Base Layer

REI Co-op

Midweight Long-Sleeve Base Layer Top

REI Co-op gear is often the best value you'll find in outdoor gear. These aren't perfect by any means, but if you want one base layer to do it all and don't want to spend a fortune, these are the base layers to get. You can have a crew top and bottom for less than a single garment of merino. The trade-off is that these aren't as warm, and they will definitely stink after you've been sweating in them all day skiing. Still, they're plenty warm enough for most activities, the fabric is pleasantly soft (and this is coming from someone who thoroughly dislikes synthetics against his skin). As an added bonus, they dry very quickly too.
They're comfortable with a tight, but not overly-tight, fit that makes them easy to layer over. I especially like the thumb loops on the sleeves, and the flatlock stitching keeps these from rubbing under load. The downside to these is they're not nearly as effective at wicking moisture as most of the other options in this guide. For that reason, these would not be my choice for more vigorous activities like cross-country skiing or snowshoeing. They're perfect for downhill skiing or hiking in the shoulder seasons, though.

• The Most Breathable Base Layer

  • Photograph: Scott Gilbertson
  • Photograph: Scott Gilbertson
    Artilect

Boulder 125 Quarter Zip Top

If your primary concern is shedding sweat and venting excess heat generated by hard physical activity, the Artilect Nuyarn Boulder 125 base layer is for you. Usually I prefer a crew top, but in this case I prefer the half zip for its added heat-dumping ability. In the right circumstance the half zip is the perfect little personal thermal regulator, and outweighs the trade-off in weight and (sometimes) comfort. Here there's no comfort sacrifice to make, as this zipper is light and well-backed to ensure no cold metal ever reaches your skin, nor does it press against your neck too much when fully zipped (one of my pet peeves).
The name here comes from the 125-gsm Nuyarn fabric (85 percent merino wool, 15 percent nylon) that makes up most of this top. Crucially though, on the sides, from the top of the arm pit down to about the bottom of your ribs, is a strip of fabric proliferated with what Artilect calls “eyelets,” tiny holes that let moisture and heat escape more easily. The result is a base layer that's better than most at shedding heat, making it perfect for high-aerobic winter activities.
The Boulder Bottoms ($120) have the same eyelets in the gusseted crotch and along the top rear of the pants, right about where the belt of your backpack sits. For this reason these are my go-to bottoms for backpacking trips where I anticipate cold mornings. The extra ventilation around the top of the pants means less sweat accumulates, and you stay drier.

• The Best Hoodie Base Layer

Want a base layer with a hood? I never did until I tried this Paka thermal hoodie, but now I am a convert. Should it get cold (even colder), you've got a hood to stop the wind blowing down your neck. When you don't need it, the thermal hoodie is just like a thermal crew—a very warm, great-looking, cozy thermal.
There are two kinds of base layers. There's the technical kind you wear because you need something that simultaneously keeps you warm and wicks moisture away from your body as you sweat. Then there are the base layers you wear because they're soft, comfy, and warm, and you enjoy wearing them around the house or when you go out for a walk in the winter. They're more versatile and stylish, so you don't look like a gorpcore poster child every time you run to the market. Paka's thermal hoodie is in the latter camp. I would not bring it ice climbing, but I wear it constantly in the winter. It's hand-made and has a cozy feel that your more technical garments do not.
That said, there are some nice features here that you would find on a more technical garment, including raglan sleeves, thumbholes on the sleeves, and a rib knit that should add to the fabric's strength. It also has a nice, relaxed fit and is plenty stretchy to allow a good amount of movement. If you really don't want the hoodie (you do), there's a crew version as well.

• The Best Balaclava Base Layer

Ridge Merino

Aspect Midweight Merino Wool Base Layer Balaclava

When the folks at Ridge suggested I try the Aspect Balaclava Base Layer, my first reaction was no, I avoid conditions where I would ever need a balaclava base layer. Ridge sent it anyway. I ignored it. Then I moved to Northern Wisconsin, and suddenly it all made sense. Below the neck, the Ridge Aspect Balaclava is like any other midweight merino wool base layer, but then it adds the hinged balaclava, which takes it up a notch. When you don't need the balaclava, it can hang out around your neck, taking the place of a neck gaiter or buff, and when the wind picks up and your nose and ears are collecting icicles, you can pull it up and protect your head and face along with the rest of you. I've come to use this far more than expected, especially on windy winter hikes.
Could you carry a separate balaclava and get the same benefits? Probably, and Ridge does sell a merino balaclava, but there are a couple of things I really like about the integrated design of the Aspect. First is the obvious: It's one piece of fabric. I don't have to remember to (or debate whether I should) pack a balaclava, it's already on me. Second, the Aspect is cut longer than almost everything else on this page, which means it stays tucked in better, which is especially handy when cross-country skiing. This is a small but valuable thing I've really come to appreciate after several winters of using it. The Aspect is 84 percent merino wool and 16 percent nylon, which is more than high-enough wool content to get all the benefits of merino, like odor resistance, sun protection, good breathability, and moisture wicking.

• The Best Synthetic Base Layer

Patagonia

Capilene Midweight Crew

These super soft and stretchy unders are made from capilene, an insulating fabric spun from 100 percent recycled polyester (note that Capilene is Patagonia's proprietary fabric and not polypropylene, which, while also polyester, is not the same). The synthetic threads perform about on par with wool. Capilene is also just about as comfortable, all while being light and quick-drying. Patagonia sells the base layers in two thicknesses: midweight and a heavier thermal weight. They come in men's and women's sizes, and the tops are available in a crewneck or collared zip-neck. I tested these in the fall in Minnesota and in San Francisco, so I wore the midweight version with a crewneck top.
Taking advantage of the precision afforded by working with synthetic fabric, Patagonia has made some interesting design choices. The garments are smooth on the outside, and have a subtly embossed diamond grid pattern on the inside. The company says this diamond pattern creates little pockets that trap heat and help wick moisture. That claim is next to impossible to verify, other than to say: The fabric did keep me about as warm as merino wool.
Like most Patagonia apparel, these fit a little looser than the same size would from other brands. Even though I tend to like my base layers snug against my skin for maximum warmth, here I appreciated the extra room in the shoulders, in the groin, and under my arms. I wore them for two days straight on a canoe camping trip—even sleeping in them—and after a wash a week later, another two days commuting to and from my office. They didn't chafe or bag out, and the elastic points never pinched. After each multiday wear, they did stink a little—more than wool would in the same scenario, but miles better than other synthetics I've tried. If you're avoiding wool because of allergies or because you're eschewing animal byproducts, this fair-trade certified two-piece is a solid alternative. —Michael Calore

• Best Sun Hoodie

  • Photograph: Scott Gilbertson
  • Photograph: Scott Gilbertson
    Paka's Sol hoodie is wonderfully soft, plenty breathable, and has proved durable as well. It offers 30+ SPF protection from that alpine glare, and it keeps you surprisingly cool considering you're wearing a long-sleeve shirt in the burning sun. There are limits to that, of course, and this one does not resist odors as well as a merino sun hoodie would, but it's better than the polyester options I've tried. I also like that it's easy to care for; just wash it cold and lay it flat to dry.
    In the summer I've been using this as my base layer. While it's a bit loose as a true base layer, pairing it with the Woolies above, and an ultralight puffer jacket makes for a good summer backpacking clothing setup in mountains or similar cooler terrain. Heading into the shoulder season I throw in a grid fleece instead since the sun isn't as much of an issue, but I've found this hoodie quite versatile, and perfect for temps up to about 75, after that I find it too much.

    Weight (Medium)	Fabric	Price
    Paka Sol sun hoodie	9.1 oz	181 gsm: 67% Tencel, 14% nylon, 14% royal alpaca, 5% spandex	$95

• Best Nontechnical Base Layer

Carhartt

Base Force Midweight Base Layer

Carhartt’s Base Force base layer is a 100 percent polyester base layer that doesn't look like a technical garment. It's what I wear around the house, on trips to the store, and working in the garage in winter. It's warm for its weight, though it is toward the thinner end of the base layer spectrum, but what I like most is the price and the fact that it doesn't look like “gear.” It looks like one of those old, cotton, long-underwear shirts with the waffle stitch, but it's not cotton, so it'll wick moisture rather than absorbing it.
At 40(oftenonsaleforless),I′mlessbotheredwhenitendsupcoveredingreaseorsawdust,andthepolyesterstandsupbettertothiskindofheavywearandwashingthanmerinowool.Don′tgetmewrong,whenI′mhikingI′llalmostalwaysgoformerino.Butwhenthefireplaceisn′tthatfarawayandI′mprobablydoingsomethingthat′sgoingtoendupgettingmyshirtdirtyortorn,thisisthebaselayerIturnto.Thatsaid,ifyouhappentoknowwhereIcangetamerino,orevenNuyarnbaselayerfor40 (often on sale for less), I'm less bothered when it ends up covered in grease or sawdust, and the polyester stands up better to this kind of heavy wear and washing than merino wool. Don't get me wrong, when I'm hiking I'll almost always go for merino. But when the fireplace isn't that far away and I'm probably doing something that's going to end up getting my shirt dirty or torn, this is the base layer I turn to. That said, if you happen to know where I can get a merino, or even Nuyarn base layer for 40(oftenonsaleforless),I′mlessbotheredwhenitendsupcoveredingreaseorsawdust,andthepolyesterstandsupbettertothiskindofheavywearandwashingthanmerinowool.Don′tgetmewrong,whenI′mhikingI′llalmostalwaysgoformerino.Butwhenthefireplaceisn′tthatfarawayandI′mprobablydoingsomethingthat′sgoingtoendupgettingmyshirtdirtyortorn,thisisthebaselayerIturnto.Thatsaid,ifyouhappentoknowwhereIcangetamerino,orevenNuyarnbaselayerfor30, do let me know in the comments below.

Honorable Mentions

There are a lot of base layers out there, including some that are great but not quite great enough to make our top picks. Here are some more options worth considering if none of the above quite fit the bill for you.

Arc'teryx

Rho LT Crew Neck

Arc'teryx’s Rho LT base layer is a 185-gsm, 84 percent polyester, 16 percent elastane shirt that fits well and is soft for a synthetic. It wicks moisture well and is nice and warm for the weight. (I’d call it a midweight base layer.)

Artilect

Flatiron 185 Crew

Artilect's Flatiron base layer is 185-gsm Nuyarn, and it fits on the tighter side, though it's plenty comfortable. I like this base layer a lot; in fact the only real drawback is that it's on the pricey side.

Kari Traa

Rose Base Layer

I am 5'2" and struggle to find clothing options that will fit—especially ones that are meant to fit next to the skin. As high-quality as a base layer may be, it won't keep you warm if it rucks up around your waist or sags below your hips. Kari Traa's leggings have a very high waist that helps keep them up. The patterns are also pretty, for those of you who object to parading around the lodge in what looks like pajamas. —Adrienne So

Ridge Merino

Aspect Long Sleeve Shirt

This is the not-a-balaclava version of the Ridge Merino Balaclava above. It's one of the rare base layers that you can actually where as just a T-shirt around town and you won't look like you just drove in from the trailhead, which makes it a bit more versatile than some of the others here. If you want something multi-use, this is a good option.

Artilect

Redstone Long Sleeve Crew

Why is Artilect so good? The company makes my favorite merino T-shirt, and now it makes my favorite base layer. The Redstone is Artilect's latest, and it's 185-gsm Nuyarn, with 82 percent merino wool. It's incredibly soft, warm, and dense. The only reason it hasn't superseded the Ibex layer is that I have woollies that have lasted 20 years, and I've only had these for about a month, but durability is the only open question. —Adrienne So

Wild Rye

Bassett Lite Raglan

Wild Rye makes fun, functional outdoor clothes for women and the Bassett set (there's leggings, too) is a lightweight merino/poly blend that's designed for highly aerobic activities. I have been using this set for running. It fits well and has features like thumbholes and flatlock seams for comfort with packs and layering. It's only 7 percent merino, however, and with all the sweating I do in it, my kid says it is starting to smell (more than I usually do). —Adrienne So

Frequently Asked Questions

What Is the Best Base Layer Material?

This will come down to what you're doing and personal preference. The three most familiar options are merino wool, synthetic nylon blends, and silk.

• Merino wool: Generally speaking, merino wool excels at keeping you warm, is nicely breathable, and makes an excellent base layer, which is why it's heavily featured in the guide. For durability, go with a blend like Nuyarn.
• Synthetic polyester blends: Synthetics have a slight edge in some circumstances, particularly if you're sweating a lot from highly aerobic activity. Synthetics don't hold as much water and consequently dry faster than merino.
• Silk: Silk is incredibly soft and does a reasonable job of wicking moisture away from your skin if you're not working too hard. If you're really exerting yourself, silk is easily overwhelmed, but for travel where you might take a long walk or go to an outdoor event in the evening, silk works well.

What Is the Best Base Layer for Cold Weather?

It really depends what you're doing in cold weather and exactly how cold we're talking. I live in northern Wisconsin. Cold to me is anything below 10 degrees Fahrenheit, at which point I reach for two layers of merino wool. In fact, I start most winter hikes wearing both our top-pick lightweight base layer and our heavy-weight base layer.

If you're in the Florida Panhandle (where I've also spent a good bit of time), you might be able to get by with just our top-pick lightweight base layer and a grid fleece or similar jacket for much of the winter.

What Is the Best Base Layer for Extreme Cold?

A fireplace. Just kidding. When you want to head out into extreme cold—say, cross-country skiing your way through the Boundary Waters in January—the best base layer is several base layers. As noted above, I often wear both our top-pick lightweight base layer and our heavy-weight base layer for winter adventures. Remember, though, that cross-country skiing and snowshoeing aren't easy. You're going to get warm pretty quickly, and you’ll be soaked with sweat if your base layer doesn't wick moisture well. For that reason, I often turn to Nuyarn, like the Artilect above. It wicks more effectively and dries faster than pure merino. Patagonia’s Capilene is also excellent for winter adventures.

Is Merino Wool the Best Base Layer?

It depends what you're doing. Most of the time I think it is, but if you're really exerting yourself or otherwise sweating a lot, synthetics may wick better, keeping you drier and therefore warmer. That said, I do not like the feel of most synthetics. Aside from testing them for this guide, I almost never wear them.

Nuyarn is a merino wool/synthetic hybrid weave, wherein merino wool is wrapped around a nylon core for warmth, lightness, and extra durability. The idea is to get the temperature regulation benefits of merino while adding some of the longevity of nylon. In my experience, Nuyarn mostly works. It's our top pick for base layers, though I find it less necessary in more casual garments where I prefer 100 percent wool.

What's the Best Base Layer for Me?

The right base layer for you is going to be the one that keeps you dry by moving your body heat and sweat away from you. Which base layer is best at this depends on what you're doing. If you're actively moving (hiking, climbing, ski touring, etc.) look for something thinner that wicks moisture better, like our top pick the Ibex Woolies Pro Tech Crew. When you stop moving and you need more warmth, throw on an extra mid layer or puffer jacket.

If you're going to been spending less time on the move, or are heading into more extreme temps, sweat is often less of an issue and the base layer is less a way to wick sweat and more of an added insulation layer. This is the scenario in which to go with a heavy weight garment like the Smartwool Classic Merino.

What if you do both? Well, then you might need two different base layers. No matter how much I want to have just one thing that does it all, the fact is nothing is that versatile. Warmer base layers like the Smartwool don't breath well enough to use on the less chilly mornings of a summer backpacking trip, where you need something but not as much as the Smartwool. At the same time the very lightweight merino layers, while great for high-intensity activities, aren't as warm when you're not moving.

If you're like me, and don't have an unlimited budget, you'll also have to factor in price. This is why I recently added the Carhartt, because while I do own the Woolies and the Smartwool Classic tops, if I wear those all the time I'll be replacing them before I know it. The Carhartt synthetic layers stand up better to wear than merino (even, often, merino blends) and cost less. The combination of the three tops is $260, which isn't too bad for a year-round system that can handle everything from summer backpacking and winter snowshoe trips to working on the truck in an unfortunately cold garage.

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Scott Gilbertson is Operations Manager for the WIRED Reviews Team. He was previously a writer and editor for WIRED’s Webmonkey.com, covering the independent web and early internet culture. You can reach him at luxagraf.net. ... Read More

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