Synthetic-Free Base Layers and Fleeces for Winter Ski and Snowboarding

Image by Paka
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Do you know the secret to staying warm on ski trips, hiking outings, and frosty morning commutes? If you live for the slopes, you probably already know the answer: it’s base layers. 

Also known as thermals, fleeces, or long johns, base layers go under your gear to help you retain body heat and stay warm in extreme weather. These are pivotal for intense skiing, snowboarding, and hiking trips in mountain climates. But Vanessa Friedman of the New York Times also recommends them for wearing under your everyday clothing to stay comfy in the dead of winter.

Unfortunately, many base layers and fleeces are made with virgin or recycled polyester, which is known to shed microplastics into the environment. These synthetics can also be harmful to your health. Polyester is dyed with azo disperse dyes which, according to Alden Wicker’s forthcoming book, are skin sensitizers and can make your skin itch or your allergies—if you have them—flair up. 

The good news is you can avoid synthetic base layers altogether by shopping for clothing with 100% natural materials. Before you strap on your ski gear and venture out into the wilderness, make sure the layers that keep you warm are also good for your health and the natural beauty around you. 

Natural Materials: Natural materials will be much better for both your comfort and the environment. Merino wool is best for base layers, as it is naturally odor-resistant, moisture-wicking, and incredibly breathable––all without sacrificing warmth. If you can’t find merino, look for alpaca wool and organic cotton. Some brands incorporate small amounts of other materials for stretch and flexibility, but you can avoid that by looking for bio-based knit materials such as Tencel instead. 

Free of Toxic Dyes and Finishes: Avoid “performance” clothing, as these are typically finished with PFAS-filled waterproofing and moisture-wicking treatments. Instead, look for natural and bio-based materials and finishes, such as merino wool and Pangaia’s peppermint oil blend. Additionally, keep an eye out for third-party certifications such as bluesign, REACH, and Oeko-Tex to be sure your base layer was made without harmful dyes. 

Ethical & Transparent Supply Chain: Look for brands that share information about their manufacturing locations and practices. Brands that conduct internal or third-party audits are more likely to ensure safe working conditions and fair wages throughout their supply chains. Keep an eye out for certifications such as Fair Trade to be sure the brand is ethical and safe for workers. 

Packaging: Single-use plastic poly bags are still prevalent, even in sustainable fashion circles. Look for brands that use biodegradable, compostable, or recycled packaging. 


All that being said, we’ve picked out and ranked our favorite brands that do plastic-free base layers for being in the great outdoors. Check them out!


What we love: Paka is a Certified B Corp that uses a blend of Peruvian alpaca wool and Tencel to create soft and flexible base layer shirts and joggers that are more sustainable than merino wool. In addition to being odor-resistant and moisture-wicking, the fabric is form-fitting and thermoregulating. All the brands products are handmade by local artisans. Paka only uses Oeko-Tex-certified dyes and ships its carbon-neutral orders in fully biodegradable packaging. 

Our review: Paka’s products are super soft and comfy, like what we would expect from alpaca wool!

Price: $75-$125



What we love: Icebreaker specializes in high-performance thermals made from merino wool sourced in New Zealand. You can pick out your perfect natural base layer by selecting the temperature conditions and the intensity of your activity. Its collection of merino wool thermals includes leggings, shorts, and both long and short sleeve shirts, in addition to basics such as underwear and socks. Icebreaker closely monitors its supply chain from beginning to end, and fosters long-term relationships with its suppliers. 

Watch out for: Some base layers contain a small percentage of elastane. Look for products marked as 100% merino wool to be sure. 

Our review: We’re long-time fans of Icebreaker here. While pricey, the styles are super comfy as well as flattering and minimalist in design. 

Price: $70-$270



What we love: Smartwool makes a variety of comfortable merino wool base layers that keep you warm without restricting movement or breathability. Its collection also includes all-season and plus-size layers to suit a variety of weather and performance conditions. Smart wool uses plant-based dyes and routinely audits its supply chain to ensure continuous improvement. Each product comes with a “sustainability roadmap” QR code that allows you to see how the brand is progressing in its ethical journey. 

Watch out for: Not all of its base layers are made with 100% natural materials. The brand still currently uses plastic packaging. 

Our review: We tried out one of its classic thermal base layer crews, and found it to be incredibly cozy and lightweight, which makes it perfect for outdoor activities. We can also say from experience that its pieces are well-made enough to survive heavy use for years. 

Price: $50-$250



What we love: Pangaia is a certified B corp that uses innovative materials that protect biodiversity while keeping you cool and comfortable. Its fleece jackets, pants, and vests are made with recycled wool, Tencel, and organic cotton. They’re also treated with the brand’s original peppermint oil blend, PPRMINT, to keep them fresh and odor-free for longer (so you can wear it multiple times in one trip.) The brand offers an interactive map of its current Tier 1 suppliers and is working toward greater transparency throughout its supply chain. Its packaging is compostable. 

Watch out for: While the peppermint oil minimizes the number of times you need to clean the fleece, it is marked as dry clean only, which we don’t recommend unless you can find a green dry cleaner near you.

Price: $220-$435



What we love: This PFAS-free and bluesign partner brand uses a blend of merino wool and Tencel to create soft and breathable sweaters and pullovers. Its mulesing-free fabrics are primarily sourced in Japan, Taiwan, Australia, South Africa, and Italy, while its manufacturing takes place across Europe. You can send old Houdini garments back to the brand for repair, or recycling after you’ve worn them out completely. 

Watch out for: There is limited information available on its packaging. 

Price: $220-$240


Kari Traa

What we love: This Olympian-founded brand offers a huge collection of merino wool base layers in a variety of styles, colors, and prints. In addition to being REACH compliant and a bluesign partner, the brand conducts internal and external audits in its factories in Vietnam, China, and Myanmar. Its non-museling wool base layers are designed to be soft and comfortable, with flatlock seams and breathable underarm panels. Kari Traa uses recycled plastic in its packaging. 

Watch out for: Not all of its base layers are made with 100% natural materials. 

Price: $30-$150



What we love: This PFAS-free Swedish brand offers a small collection of versatile, 100% merino base layers that are designed to function as wardrobe staples as well as thermals. The seams of the long johns and t-shirts are strategically placed to prevent chafing during continuous physical activity. All of Lundhags non-museling wool garments are sewn in China and can be shipped to addresses in Europe Countries. 

Watch out for: There is little information available on its dyes and packaging. It currently does not ship to the U.S. 

Price: $86-$130


REI Co-op

What we love: REI’s original brand features a line of RWS-certified merino wool base layers that are designed to be incredibly comfortable and flexible. It has flat seams for minimal chafing, and a low-profile waistband for easy layering. This collection is made in a Fair Trade-Certified factory and offers plus-sized options. You can also check its resale section to find a secondhand piece.

Watch out for: There is little information available on its supply chain and dyes. REI is currently under pressure to remove PFAS from its products, but has not yet committed to doing so, lagging behind other outdoor brands in this list. 

Price: $69.95-$89.95

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