I’d need all my fingers and toes to count the number of times I’ve reminded friends and family visiting Colorado to wear an extra sweatshirt or toss a spare jacket in their pack. Relatives visiting from the Illinois flatlands, friends from Florida, even my Colorado-born kid all get the same lecture to layer up when the mercury drops.

Experts recommend using a three-level approach to winter warmth. Rely on an outer layer to protect against wind, rain, and snow. Use a mid-layer to retain body heat. And use a base layer to wick sweat away from the body. As for which layer is the priority? “The base layer is the most important layer in a lot of ways because the real key to staying warm is staying dry at the skin level,” says Trent Bush, founder of Boulder-based outdoor brand Artilect Studio. “If you’re wet, then you start getting heat loss, and that’s where you start getting cold.”

Reliable outdoor brands typically make base layers out of either merino wool or synthetic materials like polyester, polypropylene, rayon, and nylon. (Never, ever use cotton as your base layer: It’s slow to dry, and it draws heat away from your body.) Here’s a quick guide to functional base layer fabric options:

Merino wool is a go-to option because of its thermoregulating properties. The wool fiber actually takes in water vapor from its environment—in this case, your body—and in turn releases heat, leaving you feeling drier and warmer. Plus, merino wool is naturally odor-resistant, and it’s soft next to skin due to the fiber’s fineness, which is measured in microns. The lower the micron count, the finer—and therefore, softer—the merino wool will be. On the downside, merino wool base layers tend to be more expensive and, in some cases, don’t last as long, especially if you don’t properly care for them. (Hint: Read the washing instructions on the tag.)
Synthetics are another common base layer material because of their wicking capabilities. They also tend to feel soft to the touch, stand up over time, and often come in at a lower price point than merino. Then again, synthetics can get a little stinky without frequent washing.

Another factor in the base layer selection process: fabric weight. In most instances, you’ll want to choose a thicker, more insulating base layer for colder conditions and/or activities that are less aerobic (resort skiing, for example), whereas it’s wise to select a lighter base layer that excels at wicking when you’re working up a sweat and/or in chilly, but not downright frigid, conditions.

Fortunately for those of us in Colorado, it’s easy to shop local when looking for just-right layers. Here’s a roundup of trustworthy, next-to-skin options for a range of winter pastimes, all from brands with a link to the Centennial State.

Smartwool Intraknit Thermal Max Merino

Photo courtesy of Smartwool

Best for: Resort skiing
Versions: Women’s Base Layer Pattern Hoodie, Men’s/Women’s Base Layer Quarter-Zip, Men’s/Women’s Base Layer Bottom
Price: $135 to $165

Carving down fresh corduroy and snagging freshies on a powder day are bliss-inducing endeavors—at least when you’re warm enough to enjoy the chairlift ride to the top of the hill. If you wear a base layer from the Intraknit Thermal Max Merino line, which is designed for temperatures below 25 degrees, you will be. The collection from Denver-based Smartwool uses body-mapping technology to provide a near custom fit, while still taking advantage of merino wool’s inherent moisture-managing, insulating, and odor-control attributes. Choose the hoodie for an extra bit of cozy under your ski helmet.

Krimson Klover Illustrated Base Layers

Photo courtesy of Krimson Klover

Best for: Resort skiing (and après)
Versions: Women’s tops and leggings
Price: $99 to $119

If wool doesn’t play nice with your skin, then you’ll want synthetic base layers like the Illustrated collection from Krimson Klover. Made with a recycled polyester and spandex blend, these tops and bottoms feature four-way stretch that’s ready for the back bowls and moisture-wicking properties that will help keep you dry as you work your way down the moguls. As for après, the Boulder brand’s hallmark full prints—think mountain landscapes and delightful ski scenes—will be the talk of the sun deck. Lounge away: The layers also have a UPF 50-plus rating.

Ortovox 185 Rock’N’Wool

Photo courtesy of Ortovox

Best for: Backcountry ski touring
Versions: Men’s/Women’s Long Sleeve, Men’s/Women’s Short Sleeve, Men’s/Women’s Long Pants, Men’s/Women’s Short Pants, Men’s Boxers, Women’s Sport Top, Women’s Hot Pants, Men’s/Women’s Glove Liner
Price: $40 to $110

Backcountry ski touring is an exercise in dualities, at least when it comes to exertion level. The uphill effort is taxing, but then you reach your turn-around point and stop, rest, eat a quick snack, and strip the skins from the bottom of your skis. It’s essential to have a next-to-skin layer that effectively wicks sweat away from the body and then dries quickly to ensure you’re still warm on your descent. The 185 Rock’N’Wool collection from Ortovox, which has its U.S. headquarters in Boulder, uses pure, 19-micron (i.e., very soft) merino wool that excels in these conditions. Its men’s and women’s short pants are a favorite in this lineup since they end just below the knee to kiss (but not cross) the top of your ski sock, thereby preventing seemingly innocuous yet surprisingly painful seams under your ski or snowboard boot.

Artilect Studio Boulder 125

Photo courtesy of Artilect Studio

Best for: Trail running
Versions: Men’s/Women’s Crew, Men’s/Women’s Quarter-Zip, Men’s/Women’s Tee, Men’s/Women’s Legging, Men’s/Women’s Three-Quarter Legging, Men’s Boxer Brief, Women’s Hot Pant
Price: $50 to $130

There’s no question that pounding the dirt at Boulder’s Mesa Trail or the Devil’s Backbone Trail system outside of Loveland are sweat-inducing endeavors, no matter what number the thermometer reads. So, when temps turn cold and you’re still logging miles, you’ll want a base layer that wicks effectively and dries fast. The Boulder 125 collection from Artilect Studio pushes the natural thermoregulating prowess of wool into overdrive through its use of Nuyarn spinning technology, which studies show helps a garment dry five times faster, reduces wind permeability by 53 percent, and significantly boosts durability, thermal efficiency, and stretch. “It’s warmer at a lighter weight,” Artilect’s Bush says. “And when you’re running, weight matters a lot.”

Kari Traa Fierce

Photo courtesy of Kari Traa

Best for: Hiking
Versions: Women’s Long Sleeve and Pants
Price: $60

Started by three-time Olympic medalist and champion mogul skier Kari Traa, this women’s performance apparel company excels at producing base layers for downhill pursuits. More recently, however, this Norwegian-born brand, which has U.S. offices on the Front Range, has gone off-piste and expanded into hiking apparel. The Fierce collection is designed to offer a full range of motion through a strategic panel design; these base layers are stretchy enough to handle high-stepping over icy trail hazards, and their polyester/elastane make-up means they’ll dry fast. We also love how pairing the high waistband of the pants with the top’s booty-covering drop back hem ensures the only cracks your hiking buddy will see are those in the rocks.

Ibex Natural

Photo courtesy of Ibex

Best for: Everyday (under)wear
Versions: Men’s Long Boxer Brief and Boxer Brief, Women’s Brief and Thong
Price: $30 to $60

Remember how we said merino wool is naturally odor resistant? That’s just one reason—though a pretty darn good one—it’s the perfect fiber for the base layers we don every day: our underwear. Wool fibers not only prevent the buildup of sweat and bacteria on the skin, but they also lock away odors that do form and release them only when the garment is washed. We don’t advocate wearing your undies more than once, but with merino wool you could probably get away with it. Brands like Nederland-based Ibex—which blends 18.9-micron merino wool with a touch of nylon and elastane for durability in its Natural collection—ensures these essential base layers are gentle enough for the body’s most sensitive regions.

Chill Angel Aurora Raglan

Photo courtesy of Chill Angel

Best for: Sleeping
Version: Women’s Long Sleeve
Price: $109

Betsy Seabert founded Chill Angel after a long bout of sleeplessness and extreme body temperature fluctuations, both of which were the result of breast cancer and the medication needed to fight the disease. Having worked for more than a decade at both Smartwool and sock company Point6, the longtime Steamboat Springs resident knew about the thermoregulating potential of merino wool. In 2017, she put wool’s superpowers to work in sleepwear with a line of ultra-fine, 16.5-micron merino wool pajamas. So, while the new-this-fall Aurora Raglan base layer has the performance chops to handle the trail or the slopes, we’ll be using this cashmere-esque top for the brand’s original intent: snoozing.

Pearl Izumi Transfer Wool Long Sleeve

Photo courtesy of Pearl Izumi

Best for: Cycling
Versions: Men’s and Women’s
Price: $75

Hardcore, dedicated, or just downright crazy, some people ride their bikes all year. We’re here for it! So is Broomfield’s Pearl Izumi, which has been making cycling gear for more than 60 years. Its new-in-September Transfer Wool Long Sleeve features a snug-yet-stretchy performance fit to prevent bunching under other streamlined layers. A longer back hem prevents chilly drafts, even if you’re hunched into an aero tuck.