The best base layers 2023: body-hugging tops for warmth on the trails

The foundation of your layering systems, the best base layers really come into their own in winter. Providing temperature regulation, comfort and freedom of movement, they're an essential for any hiker, mountaineer or runner. 

During the colder months, you have to strike a balance between being warm enough to be comfortable and not too hot that you start sweating once serious exertion kicks in. The last thing you want when ascending a mountain is a sweat soaked inner layer. The best base layers work hard to avoid this very situation.

Created from fabrics such as merino wool or polyester, the best base layers are fast drying, warm and effectively wick moisture away from your body, keeping you dry too. With your best waterproof jacket keeping rain out and your base layer dealing with your sweat, you've already won most of the battle when it comes to staying comfortable on the winter trails.

Our experts have put a huge array of base layers to the test to bring you this comprehensive guide on the very best options you can buy today. Our roundup features the finest merino options, including hybrids created to achieve the best of both worlds, as well as the best synthetic and bamboo base layers.

The best base layers

The best merino base layers

The Oasis – weighing in at 200 grams square meter (gsm) – is an ideal thickness for a base layer, and unsurprisingly 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 odor-resistant. 

In our tests it performed equally well for chilly trail running and trekking outings, and during a mid-winter sea paddle, though we would have appreciated thumb loops to keep the sleeves in lace.

As a natural material, merino wool is biodegradable, and the dye used is plant-based and ethically sourced. Icebreaker has never been a bargain brand, and this isn’t a cheap top. The simple designs are cheaper, but for a little extra cash there are funkier prints available too.

Read our full Icebreaker 200 Oasis Long Sleeve Crewe Thermal Top review

The Artilect W-Flatiron 185 Crew tie-dye base layer (the men's version is theM-Flatiron) may be sold as ‘warmer’, but it is actually a very hot winter base layer. Designed with Nuyarn merino fabric, it exhibits all of merino’s natural properties, but these are amplified thanks to a twist-free fibre construction. The cut is long in the arms and high in the neck, with thumbholes to prevent the top riding up beneath mid layers, and to keep wrists extra cosy. 

The base layer top has gusseted underarms with breathable panels that extend from waist to wrist. Despite having several connected panels, the seams are all flatlock stitched, meaning there is no chafing and barely an awareness that the seam is there at all. It's definitely one of the most comfortable base layers we've tested.

The tie-dye color scheme is very distinctly Artilect and it’s refreshing to see more brands step away from the standard black base layer (even though that's something of a moot point when it's covered up under a fleece and jacket).

EDZ is based in Cumbria so they know a thing or two about cold, wet weather, and they’ve come up with just the solution in this base layer. They’ve gone all in on performance and sacrificed flashy patterns, zips and thumb holes to deliver serious warmth in a classic cut base layer that looks as good around town as it does under your best fleece jacket or waterproof jacket when you’re out in the hills.

The 100% merino wool composition means this is a winner for wicking away sweat and staying dry when you’re pushing boundaries, and it remains odor-free for quite a few wears without getting wrinkly, making it great for travel, too. Though merino wool is also known for helping you stay cool in hot weather, this base layer is definitely better suited for cold weather expeditions since it traps some serious heat, and for the price it can’t really be beat. 

Read our full EDZ Merino Base-Layer review

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 odor resistance – but there is much more going on here.

The Zebru a figure-hugging bodymapped design, woven with ‘Responsive’ smart synthetic yarns including natural thermoreactive minerals that (according to Salewa) can 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. It's a tight-fitting base 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.

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.

Merino/synthetic blend base layers

With the Rho Hybrid, Arc’teryx have attempted to give you the best of both worlds offered by natural and synthetic fibres. The main fabric is their Phasic AR II, a midweight polyester that has been treated with silver ions to neutralise body odor, but there are also zoned panels under the arms made from a blend of natural merino wool and hard-wearing nylon. The result is a hybrid design does its job really well – a top that supplies great wicking performance, comfort and warmth, without any unpleasant odor.  

The Rho is an intelligently designed base layer that also happens to have one of the best fits of any long-sleeved technical tee we’ve tested. It has plenty of length in the arms and torso, plus a stand-up collar that does a great job of preventing chills from creeping down your neck. The cut is trim enough to feel cosy without being skin-tight, unlike a lot of other compression-style winter layers out there. The deep neck zip is a great way to dump a little extra heat if you’re working hard uphill too. The fabric is soft and comfortable, with very thin, flatlock seams to avoid irritation. The merrow stitching also resists snags a lot better than conventional flatlock stitching, which is a plus for durability. Another bonus is that the fabric is sleek without being shiny, so it slides easily under a midlayer fleece or puffy.

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.

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-odor 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.

Read our full Helly Hansen Lifa Merino Mid-weight Hoodie review

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 stink 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.

Best synthetic base layers

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.

Read our full Páramo Grid Technic base layer review

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-odor 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.

Read our full Megmeister Drynamo Winter High Neck Base Layer review

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 fiber 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.

Read our full Columbia Omni-Heat 3D Knit Crew II base layer shirt review

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 odor-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 does use inks that are free from PVC and phthalates, and uses ethical supply chains. Its website offers advice on how best to minimize the release of microfibers when washing garments.

Read our full Montane Dart Long Sleeve T-Shirt review

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, which we always find frustrating, but it has a high neck, which we found kept us 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.

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: in our tests it kept us warm, wicked moisture away, and absorbed very little water, letting it keep 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.

The best bamboo base layers

Cornish brand Finisterre has 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.

Read our full Finisterre Bora / Vela Bamboo base layer

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 odor-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.

How to choose a base layer

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.