Understanding Arc'teryx’s Base Layer Technology

There are those key moments in the mountains—be it a three-hour climb, puckering ski descent, or cold morning hike—when it becomes clear what's next to your skin matters. A lot. That's where base layers come in: your first line of defense against sweat, heat and cold alike. Base layers are the foundation of every outfit geared for extended time outside. At Arc'teryx, we've spent decades perfecting this foundation, because we know that great base layers don't just perform, they disappear.

The role of base layers

Base layers are the starting point of every thoughtful layering system; think of them as your second skin. While your outer shell protects you from wind, rain, and snow, your base layer (often covered in a midlayer and shell) is under it all to manage the moisture your body produces. Whether you're moving fast and generating heat or sitting still in the cold, your base layer's job is to pull sweat away from your skin and move it outward. This is critical because when moisture sits against your skin you lose heat rapidly, even in relatively mild conditions. And when it’s hot out, you likewise can’t shed heat.

A quality base layer regulates your temperature by maintaining a thin layer of air next to your skin, allowing warmth to either stay put or vent out, as a form of inner climate control. But perhaps most importantly, a high-quality technical base layer offers a comfortable barrier between your skin and the elements—one that doesn't chafe or itch, and doesn't make you bail halfway up a mountain because you’re soaked, freezing, or sweltering.

Arc'teryx's approach to base layer technology

For Arc'teryx, creating base layers has always been about solving real problems, for real people, in real places. Our approach to base-layer technology is rooted in understanding exactly what happens when you’re cresting a pass, ascending a crux, dropping a line, or even just squeezing in a lunch-break burn.

Our commitment to innovation means we're constantly testing new materials and rethinking how we construct our base layers. We've developed proprietary technologies like Phasic™, incorporated premium natural fibres like Merino wool, and developed techniques like composite mapping that strategically place different materials where they matter most. Every new improvement we make is based on one question: How does this help you be outside, in the places you love?

Smiling woman in a cap and beige long-sleeve shirt, wearing a white smartwatch, inside a tent.

Phasic™ fabric technology

Phasic™ Technology is one of our most significant innovations in base layer design, and it represents a fundamental shift in how we think about moisture management.

Traditional base layers work by wicking—they pull moisture away from your skin and toward your outer layers. But Phasic™ does this according to the natural phases of activity: active and rest. When you're warm and generating sweat, Phasic™ rapidly moves moisture outward and away from your body. When conditions cool down and you stop sweating, it retains warmth and minimizes the cooling effect of residual dampness. For stop-and-go activities, the technology essentially adapts to what your body needs in real time.

Super-wicking, hydrophobic Phi yarns speed up evaporation by dispersing moisture through the entire garment. Silver ions help keep odour at bay, while a stretch knit eliminates the need for absorbent yarn, so there’s nowhere for moisture to get trapped. You get the responsive moisture management of synthetics with the temperature regulation you'd expect from natural fibres.

Merino Wool in Arc'teryx Base Layers

Merino is a fine, soft wool perfected by nature. Shorn from a breed of sheep adapted to harsh climates, it’s organically optimized for mountain performance. It wicks moisture with remarkable efficiency while simultaneously regulating temperature with a soft feel that synthetic fibres struggle to match. It's naturally antimicrobial, which means you can wear it for longer periods without developing odour.

At Arc'teryx, we use Merino wool in specific base-layer products designed for activities where comfort and natural performance shine. Whether it's alpine pursuits or just hanging out in coastal clag, we leverage what Merino does best: keeps you comfortable through variable conditions with minimal fuss.

Upper body of a person wearing a dark gray textured long-sleeve shirt with visible stitching.

Real-world applications

For a summer hiking trip in variable weather, you might reach for a lightweight synthetic base layer—something that dries quickly and handles rapid moisture swings, like the Rho LT Crew (women’s Rho). For a multi-day alpine climb where weight matters but conditions are consistent, a Merino blend offers superior temperature regulation and the confidence that you won't need to wash it halfway through. For women, something like the Satoro Merino Wool Crew Neck might be best here. For winter climbing or ski touring, where you're moving through significant temperature changes and extended periods of exertion, our heavier Merino or Phasic™ options keep you dialed in from dawn until dusk. Check out the Women's Rho Bootcut Bottom (men’s Rho bottom) for a great example of that.

The key is matching the base layer to both your activity intensity and the conditions you're expecting. Understand your effort level, consider the temperature range you'll encounter, and think about how long you'll be wearing the piece.

Care and maintenance of Arc'teryx base layers

Always check the care label of the garment for exact guidelines. For Merino and wool products in general, we recommend dry-cleaning or hand washing in cold water with a light, scent-free detergent. Dry on low heat or lay flat to dry naturally.

For synthetic garments like fleece, also check the exact guidelines of the care label. We recommend machine washing in lukewarm water, keeping garments of similar colour together. Don’t use fabric softeners or bleach, which compromise the technical properties that make these layers special. Do not iron or dry clean. For optimal performance, add your fleece garment to the washing machine when you wash your GORE-TEX jacket using Arcteryx Nu Detergent. It will remove all of the dirt, prevent odor from building up in the fabric and leave no residue. Turn the base layer inside out and tumble dry at a low temperature.

How you care for your base layers directly impacts how well and long they'll perform for you. Be kind, and they’ll last you a long time!

A great base layer does its job quietly. It just works, keeping you comfortable and dry so you can focus on your line, climb, or chill moments without feeling chilled.

Arc'teryx's approach to base-layer technology is built on decades of listening to athletes, testing in real conditions, and constantly asking how we can do better. Through innovations like Phasic™ Technology, the timeless performance of Merino wool, and precision techniques like composite mapping, we've created base layers that perform across every condition and for every activity, while simply disappearing against your skin.

Learn More:

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Shop Women’s Base Layers

2025-12-01