The best base layer: for winter walking, running, hiking, biking and skiing

The best base layers in this guide are the bedrock of the layering system, which, as every outdoorsy type will tell you, is the secret to staying warm when you leave the house in the colder months, from late autumn through winter and into spring.

Don’t make the mistake of regarding base layers as just another piece of underwear. There’s a lot going on in the design and materials used to create the highest performing and best base layers, and you need to think about what you need them to do for you when you’re engaged in cold play of one sort or another, whether you’re a walker, runner, hiker, biker or all-season camper.

• Get your outer layer sorted with the best waterproof jackets
• Think mid layers with the best down jackets and puffers
• Discover why layering is important with this advice

When looking for the best base layers, pay close attention to the style, features, thicknesses and the materials used. Don’t just go for the thickest garment out there – it might be too hot for what you’re intending to use it for, and the conditions you’re likely to encounter. And besides the all-important thermal properties of the top, also consider comfort, coverage area, moisture management and features such as zips.

Here we’re looking at the best base layer tops – matching thermal bottom layers are sometimes available from the brands featured, and you might want to check these out if you’re intending to venture out in very cold conditions for an extended period of time.

The polyester-based Parameta G material used to make this well-thought-through top features an ingenious raised-grid pattern that, when another layer is added on top, traps air between the squares. This air then becomes warmed by your body heat, providing a layer of thermal insulation. Clever. If you get too hot, you can quickly release this air by taking off (or just unzipping) your mid layer or outer layer. Alternatively, in warmer conditions or during high intensity activity, the Grid Technic can be worn on its own, when it works as a standard poly top, providing decent levels of warmth (even when wet) and excellent moisture wicking properties. The Grid Technic has a high neck to keep your throat warm, which features a mid-length zip (with a good chin protector), so you can let cool air in when needed. It also has thumb hoops, so the base layer won’t ride up your arm when you pull another layer over the top, and your wrist won’t become exposed between the top and your glove. You shouldn’t suffer a chilly lower back, either, even when wearing a backpack, as the top is longer at the rear. The athletic cut means it fits closely (no annoying excess material flapping around) and the next-to-skin comfort is good, if not quite as luxurious as merino. As with the vast majority of Páramo garments, this top is made ethically in Colombia with the Miquelina Foundation (opens in new tab), a member of the World Fair Trade Organization, and it is fully recyclable through Páramo.

Clever Kiwi company Icebreaker blazed a trail with the production top-quality and stylish merino products, and this soft high-performing wool is the perfect material for a base layer. The Oasis – weighing in at 200 grams square metre (gsm) – is an ideal thickness for a base layer too, and unsurprisingly this is one of the company’s best selling garments. Made from 100% merino, this top is supremely comfortable, wicks moisture away with aplomb, maintains most of its thermal properties when wet and is naturally antimicrobial, and therefore odour-resistant. As a natural material, merino is biodegradable, and the dye used is plant-based and ethically sourced. Icebreaker have never been a bargain brand, and this isn’t a cheap top. The simple designs are cheaper, but for a few extra bob there are funkier prints available, including one featuring images of a melting Greenland icecap, shot by New York City–based artist and photographer, Justin Brice Guariglia, well known for his work about climate change.

Although it does feel slightly strange, and extremely clingy, the seamless design of this technical top from Dutch brand Megmeister (German for master craftsman) offers sensational next-to-skin comfort. Constructed in Italy from a mixture of manmade base materials, including elastane, the Drynamo is extremely close fitting, with zero excess material to flap around or get in the way. The polypropylene dryarn element of the fabric cocktail means the top maintains its excellent thermal properties, even when wet. It is super light, wicks moisture away from your body well and has also been given antibacterial and anti-odour treatment. The high neck is a nice touch, providing extra warmth. On the downside, it lacks thumb hooks, and occasionally it rides up your back.

Helly Hansen pretty much pioneered the concept of technical, high-performing base layers, and they remain industry leaders when it comes to making good stuff that will keep you alive in challenging conditions, as the double-layer Lifa Merino Hoodie perfectly illustrates. ‘Lifa’ is the brand’s own high-performing polypropylene yarn, which is used in almost equal measure here with merino wool. Both fabrics excel at doing all the things you want a base layer to do – they wick moisture away from the body and have excellent thermal qualities even when wet – but each also brings its own tricks to the party. The merino brings with it natural antibacterial and anti-odour properties, while the Lifa is more hard-wearing and helps keep the top in shape. A really comfortable top, with flat seams, this is the only base layer on test that had a hoodie, which people will either love or hate. If you’re out and about in seriously cold conditions, your ears are going to love it – it fits under climbing or bike helmet no problem, and really adds to the protection level of the top, making it suitable for high level epics on serious mountains. If you’re adventuring at a more modest level, this is still a lovely top, but you might find it a little too substantial to wear as a base layer.

Although it has a pretty pedestrian appearance when being worn, if you turn this top inside out, it looks almost metallic, and resembles something you might see worn on the bridge of the starship Enterprise. As with everything they make these days, Columbia have employed their trademark Omni-Heat technology in this base layer, in a bid to keep the wearer warmer than any other brand. The Omni-Heat concept involves the use of loads of soft fibre pods, which create a little gap between the garment being worn, and your skin – your body heat then warms the air trapped inside this space, and the silver lining of the top reflects this heated air back at you. Genius. In addition, because there’s a space between your body and the base layer, less moisture builds up, and the poly fabric of the top wicks sweat away too. This all sounds impressive, but it does actually work too – in fact, it works so well that sometimes you can feel hot in this top, although shedding an outer layer generally sorts that out. If you’re heading somewhere seriously cold – like a mountain top, or a ski resort – this is a great option. It’s made with material with four-way stretch, so it allows plenty of movement, has non-annoying flat seams, and has been treated with an antimicrobial substance, to prevent bacteria and BO building up. Other features include integrated inner-sleeve thumb loops (as opposed to thumb holes, which would let cold air in) to stop your arm getting exposed when you don another layer, and a long torso, to prevent the top riding up and revealing your back or stomach to the elements.

Super lightweight, this fully synthetic top is a no-frills base layer that offers versatile functionality and performance without all the bells and whistles. You can wear it whatever you’re doing – walking, cycling, running, canoeing, climbing – and being so light, it’s the perfect top to throw in a backpack ‘just in case’ you might need another layer. The manmade material maintains its thermal properties event when wet, because it absorbs very little water, which also means it doesn’t get significantly heavier when damp, and it will dry quickly. The downside to synthetic tops is that they tend to get a bit stinky after time, but the dart has been treated with an odour-control agent to stop this happening. For a simple top, it has a nice design, and for a few more quid you can get a version with a half-length zip, for quick venting if you get overly warm (there’s also a short-sleeved version for summer for £26). It does lack a few little touches, such as thumb hoops, but it’s a good top for a good price. While the materials used are not eco friendly, Montane do use inks that are free from PVC and phthalates, and employ ethical supply chains (opens in new tab), and their website (opens in new tab) offers advice on how best to minimise the release of microfibers when washing garments.

Cornish brand Finisterre have long offered a range of merino underwear, but they’ve always been an environmentally conscious company, and last year they added bamboo base layers to their range. A natural product, bamboo is both sustainable to produce and the end product will eventually biodegrade, unlike synthetic poly tops, which will outlast us all and release micro fibres into the water system and food chain every time they’re washed.  Bamboo garments are also wearable for vegans. And the material performs too – it’s highly breathable, doesn’t chafe, is naturally antibacterial and pong resistant, wicks moisture away, feels lovely next to your skin, and offers decent thermal properties to keep the wearer warm. On the downside, the thermal performance drops more when it’s wet than either synthetics or merino (especially when mixed with cotton), and it gets quite a bit heavier. But this is a very comfortable top, with ergonomic flat-locked seams. By design it is looser fitting, and therefore offers plenty of freedom of movement during activities, but we think thumb hoops would have been a good addition. It’s also available in a short-sleeve version.

Named for Monte Zebrù in the Ortler Alps, this top is exceptionally light, but it punches well above its weight when it comes to performance. The majority-merino material offers everything that wool always brings to the party – breathable with excellent moisture-wicking capability, the ability to keep you warm when its cold and cool when it’s hot, natural odour resistance – but there is much more going on here. The Zebru has been made to a figure-hugging bodymapped design, woven with ‘Responsive’ smart synthetic yarns including natural thermoreactive minerals that – so Salewa say – boast the ability to absorb Far-infrared radiation (FIR) from your body and slowly release it back into muscle tissue, leading to better blood flow, improved oxygenation, longer-lasting warmth, enhanced performance and faster recovery. This all sounds very impressive, even if it is impossible to monitor, but having tested this top on the trails, we can attest to its excellent performance levels. It is a tight-fitting layer, but the four-way stretch material means you can move easily while wearing it, and the next-to-skin comfort levels are good, with flat-lock seams causing no rubbing or annoyance. It is also styled long, so it doesn’t ride up your back, but disappointingly it lacks thumb hoops.

There’s a lot of top and a fair bit of tech in the Berghaus Thermal Tech Tee, which feels almost too substantial to be a piece of underwear. You can, of course, wear it as a stand alone garment, but it is designed as a base layer. It’s made from a synthetic poly yarn the British brand call Argentium (opens in new tab), which contains recycled silver and packs special powers, including antibacterial properties, which stop the top getting stinky. It’s also breathable, it wicks moisture away from the body and maintains its excellent thermal properties even when wet. The top lacks thumb loops, but it has a high neck, keeping the wearer warm right up to the chin. There’s also a half-length zip, so you can dump excess heat if you start to feel a bit hot under collar.

Made from a magical mix of merino and manmade polyester (32% of which is recycled), this simple-looking top is a lightweight, high-performing base layer that does everything you can ask for. The athletic-fit Forge keeps you warm (even when wet), dries quickly, wicks moisture, refuses to pong even after extended wear and keeps its shape. It will serve you well out on the trails all winter, worn as an active undergarment, but at this weight, it’s one of those pieces of kit that’s well worth stashing in a backpack (or even a hydration pack) all year round, in case a change of conditions catches you out and you find yourself in need of an extra layer. The only thing it is missing is thumb hoops, to stop the top riding up your arm when you pull on another layer.

At first glance, this thermal top looks fairly basic – it’s here to do a job for a fair price with no bells and whistles, true enough – but there’s more of a backstory to these base layers, because they are made from recycled plastic. Around 10 to 12 discarded bottles go into each garment, and while we know microfibres still get released every time synthetic tops are washed, it’s certainly better to buy something recycled. Craghoppers’ sustainability policies (opens in new tab) are solid, and the brand also guarantee their garments for life (as in, the clothes expected lifespan), and will take used garments back to recycle them once they’ve been worn out. A relatively thick top, its performance levels are excellent: it keeps you warm, wicks moisture away and absorbs very little water, so maintains its warmth-giving capabilities even when wet. On the down side, it lacks thumb hoops, but it is available in a short-sleeve iteration, for year-round use.

Made mainly from high quality 200gsm merino wool, this base layer from Scottish brand Keela is a high performing under garment, which provides heat when outdoor conditions are cold, but is also capable of keeping you cool when the outside temperature rises. Such is the magic of merino, which also brings anti bacterial properties to the table, to stop your top smelling bad. It also breathes well, wicks moisture, and feels luxuriously comfortable next to your skin, especially with the flat-lock seams this top boasts. Well designed all round, the Keela base layer is close fitting and features a high neck, for extra warmth, complete with a zip (and chin protector), so you can let cool air in during high-intensity activity. It’s also long fitting, to keep your lower back covered, but lacks thumb hoops.

The bamboo-based fabric used in Bam garments is lovely and comfortable next to your skin, and causes no chafing or itchiness, which can’t always be said of synthetics or wool blends. Bamboo is also breathable and has odour-resistant properties, it wicks moisture away well, and provides good thermal insulation when it’s dry – less so when it’s wet, though, and the cotton in the mix doesn’t help, even if it is organic. Bam is working towards a self-imposed target to be impact positive by 2030 (opens in new tab), and this top has strong environmental creds. The design is classy too – there’s a half-length zip so you can vent if things start to heat up, with a little zip-garage to prevent skin or beard hair getting caught, and the wrists have robust thumb loops, so sleeves can be secured in place when adding an extra layer or wearing gloves. This top has a less athletic fit than others on test, but some people will prefer a looser feel.

What to look for in the best base layers

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 insulation

The best base layers work by trapping air, which is then warmed up by your body heat to provide a thermal layer. For this to work well, the garment must be made from a material that holds on to air well, but gets rid of water quickly.

Materials

Natural fabrics – especially merino wool, but also bamboo – work very well in the best base layers, but you’ll often see manmade materials like polyester and Lycra employed in the mix, and these can help make the garment closefitting (as a base layer should be), maintain its shape, add to its durability and improve the all-important thermal performance, especially if it gets wet. Merino wool is a magic material that keeps you warm when you need it to, but can also cool you down when outside conditions are hot. It also wicks moisture away from your body, feels comfortable and boasts antibacterial properties, which stop tops from getting too smelly. Garments with a high percentage of cotton should be avoided, as cotton holds onto water and performs terribly when wet, losing all its thermal properties and keeping you cold.

Comfort

Next-to-skin comfort is very important in a base layer, for obvious reasons. Most people find merino wool extremely comfy, but others prefer bamboo, or synthetics such as brushed fleece. This is subjective, but worth getting right, otherwise you’ll spend all your time itching. Tops with flat-lock seams will be more comfortable to wear.

Fit

Ideally, the best base layers need to hug you tight. You don’t want the back of the sleeves riding up to expose bare skin to the cold, and a top that wrinkles under another layer won’t be comfortable.

Features

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

While outer layers have to cope with mist, rain and snow, base layers must deal with sweat, so they need to be breathable and have the ability to wick moisture away from your body.

Weight

Base layers are often ascribed a weight (for example, ‘midweight’), which relates to the thickness of the piece of clothing in question. Obviously, the higher the weighting, the warmer the garment will be. It’s definitely possible to have a base layer that’s too hot, so go with an option that best suits the type of outdoor activity you do most often, in the kind of conditions you’re most likely to be out doing it in.

Durability

While merino wool is one of the best base layer materials, it does only last so long and it can lose its shape, which is why many brands use a mix of wool and hardier synthetic fabrics.

Environmental concerns

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.

Our guide to the most eco-friendly outdoor brands will point you in the right direction.