The Best Base Layers for Every Adventure

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 to this one, 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.

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.

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), and, 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.

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.

These soft and stretchy unders are made from capilene, an insulating fabric spun from 100 percent recycled polyester. 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

We have an entire guide to sun hoodies in the works, but this is our favorite so far in testing. 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.