Our tester wore this on a thru-hike of Arizona’s 480-mile Mogollon Rim Trail in October and an Iceland traverse in August and raved about the Wolverino. Its durable mix of itch-free wool, and fast-drying synthetic fibers and design features gave us everything we want in a base layer. It's a personal preference what kind of base layer you want. We note when a model is available as a crew or a zip or both. Features 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. I’ve always prioritized the gear on the outside but with time I’ve discovered that one of the best secrets for truly keeping kids warm is the layer on the inside.

Reasonably priced given its sustainability credentials (it’s made from 100% recycled polyester fibres), this top is best kept for wintry wear when strolling round the park or popping to the shops. I must admit that I use thumb holes a lot and can find a few persuasive benefits to them (Image credit: Emily Woodhouse)Designed with dynamic outdoor exercising such as trail runs or hikes in mind, the Terrax Drynamo has an interesting feature – small holes under the armpits to aid ventilation and regulate your body temperature. The sleeves and torso, however, come up on the longer side, so it’s best suited to taller people. The Patagonia Capilene Midweight excels as a baselayer compared to other synthetic layers we considered. It’s comfortable, which is an essential aspect of next-to-skin layers. The Cool Daily is also treated with a Polygiene anti-odor technology called HeiQ® Fresh Durable Odor Control, which seemed to work even after a week of continuous use. The fabric is 50% recycled, bluesign certified for environmentally-friendly dying, and sewn in a Fair Trade factory. The best merino wool base layer we tested is the Ibex Woolies 2. Both Liz and Naomi tested this base layer seven years ago, and both of them consistently reach for that same shirt at least once a week. Since then, Ibex has gone through a major rebranding, but for 2023, it has re-released the Woolies. We are overjoyed. We're thrilled to report it has all the same great features we loved with the previous version. Although synthetic baselayers dry fast when wet, they do not keep you as warm when they are wet and can often leave you feeling clammy if the material doesn’t have airflow to dry.

The main difference between the two options is that the adventure onesie is made with a mid-weight wool while the Ik’splor set is thinner. The onesie might be the preferred option if you are in frigid temps or want a looser fitting mid-layer. One pivotal trend centers around the ethical treatment of animals and environmentally conscious practices in wool production. Brands increasingly opt for responsibly sourced wool, signifying a commitment to humane treatment and stringent environmental standards. This is exemplified by certifications like the Responsible Wool Standard and ZQ-certified wool, assuring consumers that the well-being of sheep and the environment is a top priority. Responsible wool sourcing not only aligns with ethical principles but also contributes to a more sustainable supply chain. Recycled synthetic materialsWee woolies is a company based out of Vancouver, BC that prides themselves on being a completely natural product through and through. For a lightweight, affordable, and highly UPF-protective base layer, we think the Mountain Hardwear Crater Lake Hoodie is the best of all worlds. With a UPF rating of 50+, the lightest and thinnest fabric we tested, and sizes ranging from XS-3X, the Crater Lake hoodie is everything we want in a base layer for hiking. The Mountain Hardwear Crater Lake Hoodie is our winner for Best Base Layer for hiking. It's also the overall winner in our Best Sun Shirt guide.As a 100% synthetic base layer, it’s also suitable for vegans or people allergic to wool. Due to the natural odor resistant properties of merino, your merino pieces can go quite a while without a washing. They do NOT need a wash after every wear. TMM Team Member Jami only does a wool clothing load every 3-4 weeks, depending on use (and that’s even on her sweaty running Merino!). Pros: Synthetic base layers tend to be affordable, lightweight and easy to wear. They can feel similar to Lycra, making them a good fit for activities requiring a wide range of motion, such as HIIT. Heading out for a casual bike ride or ramble? Look no further for your perfect base layer. Our panel was impressed by its temperature-regulating ability, saying it felt pleasingly warm to wear, and loved its choice of four designs.

These mixed blend items are great for higher intensity aerobic activities when you still want the best wool properties but want to stay drier.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. Not really. I know I’ve mentioned a few good benefits of thumb holes in your outdoor gear, but let’s be honest, we all fared perfectly well without them before. You can always keep your hands warm on a run or a hike with gloves, and though I’ve heard runners say they like thumb holes because it stops their sleeves from riding up, I can’t personally say that’s ever a problem I’ve encountered. Maybe I don’t run swiftly enough? Most synthetics can be tumble dried on low, but air drying is best for some pieces. Conclusion/Summary The Smartwool Intraknit Thermal Merino wins top honors for its weight class thanks to its innovative seamless knitting technology that blends swaths of warm fabric with panels that add durability and ventilation — all without requiring additional seams, which saves on weight and bulk. We think this is a pretty cool innovation, and it seems to work. The slim, athletic fit excels as a base layer, allowing you to top it off with additional layers for a complete system to prepare you for the harshest of conditions. Extra long sleeves, torso, and a drop tail hem ensure that the Intraknit Thermal covers you no matter how you move. The midweight Merino wool blend fabric is a great "just right" weight to use for most cool to cold days outdoors.