Weak durability keeps this top a dedicated base layer, seams found converging in pinch points, pricey Slim athletic fit requires a slim athletic body type, expensive, not as durable as cheaper synthetics Main fabric: Phasic AR II (100% polyester with DAO finish), Zoned panels: Nucliex 150 (87% Wool, 13% Nylon, RWS wool) The Solution 150 won't be a perfect fit for everyone: the slim fit can be too tight for many body types to wear comfortably — especially if you're worried about the sleeves being too tight around the shoulders and pits. The NuYarn wool blend is a thin, stretchy fabric, but durability is a concern if worn alone and not safely underneath a top layer. Finally, we need to talk about the price: this is one of the most expensive base layers we've tested. Still, if you can swing the cost, you may never find yourself not wearing this hoody, from when the first flakes fall to when the last ski run closes. Our tester felt the sizing was somewhat generous, with extra room on the waist and arm length; she reports that a small felt more like a size 12 – so this is worth bearing in mind if you’re after a more fitted top.

For a decade, our team of experts has bought and tested dozens of the best base layers on the market. For this update, we compare 17 of the most popular options side-by-side. From the ski slopes to alpine climbs to sleeping out under the stars, our in-depth analysis derives from real-world adventures undertaken while wearing each model. We score all base layers across key areas of performance, like warmth, breathability, and drying speed. Whether it's for the warm or cold season, a quality base layer is sure to keep you dry and comfortable, no matter where your next outdoor escapade takes you.

Lightweight base layers are less likely to have them, but in a more substantial base layer, a partial-length zips is an excellent feature, allowing you to dump excess heat during activities. We like thumb loops too, which stop sleeves from riding up when you put on another layer, and prevent gaps appearing between your top and your gloves. Moisture management Thin and lightweight Merino blend, 1/4 zip enhances thermal regulation, extra long sleeves and torso

Trail runs were incorporated into our test plans to assess breathability and versatility. Though silk offers a higher warmth-to-weight ratio than other fabrics, it is less breathable than other natural fibers. It’s tempting to go cheap on your base layers – after all, they’re not generally the most exciting bits of kit. But we think a top-quality technical layer like this one is well worth it. As mentioned, the Cotopaxi Liso isn't the warmest option, as it's thinner and less warm than many of its rivals. It's also less warm than wool shirts of the same weight. If gone unwashed, the synthetic fabric will develop a funk if you after a few days of wear, despite the Polygiene application applied to the fabric. Be mindful when washing the Liso: all that stretch is accomplished by using a hefty amount of spandex in the fabric, and this will lose its stretchiness after enduring too many dryer cycles. If you want a great budget wool top, have a look at the Meriwool Merino 250.

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These types of questions will help guide you in the direction of what holds more importance for you as a buyer. Decide which metrics are most important for your sport or activity—whether that's ice climbing or shoveling snow in your driveway—and base your decisions on those factors first.

As always, the most sustainable clothes are the ones you’ve already got, but if you do need to invest in a new base layer, look for garments woven from natural, biodegradable materials (wool, bamboo) or recycled synthetics, made with natural dyes by brands with good environmental principles and robust manufacturing ethics. While there are myriad styles to choose from, the best base layers are there to do one job well: keep the wearer warm and safe. Additional features will add comfort and functionality, but the thermal properties are the most important factor. The following are some things to consider. Thermal insulationOne of our favorite super stretchy, soft, and warm synthetic base layers for cool to cold conditions You may be surprised to discover that you actually don't have to pay an arm and a leg for a superb Merino wool top. The Meriwool Merino 250 Long Sleeve offers near-top-quality performance at a fraction of the cost of most of the 100% Merino tops we tested. Even though it is firmly in the midweight category, the extra-fine spun wool used to create this layer is more breathable than other directly comparable models, making it a great option for folks engaged in high-output activities like ski touring. Couple that with a slim, stylish fit, and you have a layer you can take from the mountain straight to après-ski.