Thermals, long johns… whatever you want to call the best thermal underwear for women, there’s nothing like a warm layer worn next to the skin to help keep the chill of winter at bay. Whether you’re off skiing, hiking or cold-weather camping, layering up is the best way to trap in heat and keep cosy in the great outdoors – and a good layering system starts next to the skin, with the best women’s thermals – both tops and leggings.
You can choose thermal garments constructed from various comfortable and cosy materials. You’ll find our full buyer’s guide below for help on how to find your perfect thermal set, but among our top picks are BAM’s soft bamboo cold bashers, Icebreaker’s moisture-wicking Merino wool options and Odlo’s eco-friendly recycled polyester thermals, which all really stood out on test.
If you don’t find what you’re after here, check out our guide to technical base layers and/or running underwear.
The best thermal tops for women
Merino really is a bit of a wonder material for thermals and base layers – it’s naturally warm but breathable and it wicks away sweat, so it’s perfect if you’re getting active.
It also naturally resists odors – ideal if you’re camping or skiing in the backcountry for several days at a time, without the luxury of changing your base layers – and it is soft and comfy against the skin, unlike other wool base layers, which can be scratchy.
Merino can be expensive, but we reckon Keela’s simple, crew neck, long-sleeved base layer is well worth its sensible price tag – it’s smart, easy to wear with everything, great quality and should last you for years of outdoor adventures.
Ultra-comfy, organic and highly breathable, bamboo is a fantastic material for sportswear. And BAM’s sport-friendly base layers aren’t just comfortable – they’re smart enough to wear as regular tops and leggings when you aren’t out on the trail.
The stretchy Perform top is supremely comfortable and moves when you do whether you’re walking, climbing, skiing or cycling. We also love the thumb holes, handy for trapping warmth in and keeping sleeves in place if you’re wearing gloves on top.
Effective antibacterial properties make bamboo a clever choice for camping or backcountry expeditions: you can hike for days in this anti-odor base layer jersey without offending the noses of your hiking companions.
A firm favorite with gym fans and sporty types, Under Armour’s Cold Gear range is designed for use in the winter months, and can be relied on when temperatures drop.
A simple design and a flattering fit make this mock neck top a pleasure to wear, and we found the great stretch was ideal for more vigorous activities, where you don’t want to notice you’re even wearing a base layer as you move.
What’s more, although polyester is not a very eco-friendly material, of all the base layers we’ve tested, the Cold Gear top proved the fastest to dry, and the best at wicking away sweat. Perfect for anyone who likes to get really active in the great outdoors in milder winter weather.
Cornish brand Finisterre make great quality outdoor kit in nature-inspired colors, and their bamboo range of thermals and base layers are stand-out pieces for winter layering.
We like these soft neutral tops (they also do matching bottoms) because they work so well as casual day-to-day clothing as well as for active adventures, unlike sportier-looking base layers. The bamboo wicks away sweat brilliantly and is a vegan option, unlike Merino wool.
This bamboo layer has some stretch but is quite tight-fitting, so you may want to pick a size up if you like a boxier fit. Wear this breathable top in the shoulder seasons; if you need an alternative for colder winter weather, Merino has sets designed for that too.
The best thermal bottoms for women
Keep the bottom half of your body super snug in these woolly tights. We love wearing these Alpspitze leggings as a base layer for walking and skiing – they’re delightfully warm, they stay put all day, they’re highly breathable and they sport a great wide waistband so comfortable that you’ll barely notice you’re wearing them.
Unlike synthetic bottoms, these wool leggings have a soft, natural feel against the skin. They’re also treated with an anti-bacterial treatment that keeps them feeling – and smelling – fresh even if you do get sweaty.
These are firmly in the “underwear” rather than the “leggings” camp – it’s a pity they’re too thin and see-through to work alone as workout bottoms, but as breathable long johns they’re a great quality choice.
The best thermal top-and-bottom combos
We’ve put the Blackcomb thermals through many months of outdoor adventures, and they’ve never let us down. These soft synthetic garments are comfortable and form-fitting (yet still flattering), with a ribbed shape that stays put all day – and they’re so light it barely feels like you’re wearing anything at all.
They’ll keep you snug in snow, but are breathable and comfortable enough to wear alone, and they’re durable too: we’ve washed them multiple times and they always come out looking and performing like new. Tops are available with and without high necks, and with an optional face mask built in for the coldest climates.
The new Eco versions of the Blackcomb collection are crafted with recycled materials.
Buy the Odlo Women's Blackcomb Eco Long Sleeve With Facemask
Buy the Odlo Women's Blackcomb Eco Bottoms
On bitter winter days when you’re skiing up a storm or trekking to windy mountain tops you’re going to need base layers that go the distance. Enter Icebreaker’s 250 range.
These thicker, heavier and very warm base layers are less breathable than lighter thermals but they offer instant welcome warmth and can really make a difference when temperatures drop. We also like sleeping in them on winter camping trips.
Merino wool once again offers a comfortable, moisture-wicking and antibacterial triple whammy. Last but not least, the Vertex top and bottoms look rather fetching, in bold geometric designs that Icebreaker call “Fractured Landscape”.
Buy the Icebreaker Women's Merino 250 Vertex Long Sleeve Crewe Thermal Top Fractured Landscapes
Buy the Icebreaker Women's Merino 250 Vertex Thermal Leggings Fractured Landscapes
A cult favorite among fitness bloggers, Sweaty Betty’s retro-looking thermals bases aren’t just good-looking, they’re also wonderfully comfortable and warm to wear.
These synthetic knitted layers are primarily aimed at skiers, but the seamless design means they won’t dig in anywhere, so they’re ideal for sports and fitness, as well as providing warmth when you’re out and about.
We particularly like the high waist and wide waistband on the leggings and the zip neck of the top. Our only criticism is that the insides of these thermals are quite delicate – they need gentle washing, and threads can come loose or snarl up if you catch them on jewellery.
Buy the Sweaty Betty Ski Jacquard Base Layer Leggings
The best thermal onesies
Okay, so it’s cute, but before you write off Mons Royale’s Monsie as a style-focused option, take a closer look.
The New Zealand brand call their one-piece “the ultimate base layer”, and it’s actually a pretty clever choice – it’s made of 100% Merino wool, for great softness, moisture wicking and breathability, and on test we found that wearing an all-in-one did trap in more warmth than two separate pieces.
A front and rear zipper make it easy to ventilate the suit (and to stop for loo breaks), the hood protects your head and at just 190g this suit won’t weigh you down. Plus, the Monsie looks enough like casual clothing that you can lounge around it in at après ski.
Coolest base layer for warmer weather
Most base layer tops we recommend have long sleeves, but when you’re hiking in changeable conditions in spring and fall they can be overkill.
Montane’s Dart T-shirt is a great versatile base layer that can be worn alone to keep your core warm in warmer weather, under a light mid layer in the shoulder seasons or just down the pub with jeans when you’re back from the hills.
Round neck or zip neck versions are both available. At a smidge under £30 each it’s definitely worth adding one to your base layer collection for chilly but sunny days.
| Thermal underwear | Price | Main material | Sizes | Style |
| Keela Women’s Merino Round Neck Top | $54.54 (US) / £54.95 (UK) / $81.30 (AU ) | Merino wool | 8-20 | Round neck top |
| BAM Perform Bamboo Top Base Layer | $53-$60 (US) / £39-£44 (UK) | Bamboo | 8-16 | Round neck top |
| Under Armour ColdGear Authentics Mock Neck Top | $53.59 (US) / £45 (UK) | Polyester | XS-XL | Mock neck top |
| Finisterre Vela Bamboo Long Sleeve Base Layer | $59.55 (US) / £50 (UK) | Bamboo | 6-18 | Round neck top |
| Jack Wolfskin Alpspitze Wool Pants | $95 + $83 (US) / £80 + £70 (UK) | Merino wool | XS-XL | Three-quarter length leggings |
| Odlo Blackcomb Eco Face Mask Top and Bottoms | $95 + $83 (US) / £80 + £70 (UK) | Recycled polyester | XS-XL | Face mask neck |
| Icebreaker Vertex Merino 250 Top and Bottoms | $130 (US) / £110 (UK) | Merino wool | XS-XL | Round neck top |
| Sweaty Betty Ski Jacquard Base Layer Top and Bottoms | $95 (US) / £80 (UK) | Polyamide | XS-XL | Half zip top |
| Mons Royale The Monsie | $209 (US) / £175 (UK) | Merino wool | XS-XL | Zip neck onesie |
| Montane Dart T-Shirt | $33 (US) / £28 (UK) | Recycled polyester | 6-18 | Round or zip neck |
How we test women’s thermal underwear
Our testers have used the best thermal tops and thermal leggings for women on cold-weather hikes and ski trips, and compared them for warmth, breathability, comfort, cost and durability.
How to choose women's thermal underwear
What constitutes the “best women’s thermal underwear” largely comes down to personal preferences, but comfort and functionality should really take precedence over fashion, since they’re not usually going to be a garment that you’re seen in out in public. We recommend that you take the following factors into consideration when looking for the best women’s thermals for you.
Fit
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It’s definitely worth trying thermal base layers on in person, especially if you’re on the tall or short side – they should hug your body without feeling too restrictive around the waistband, ankles, neck or sleeves. Some base layers are stretchier than others – we reckoned thermals with some stretch offered more warmth on test, as there’s no empty space between the fabric and your skin for the cold to creep in. When you try on leggings and tops, check that you can move your arms and legs freely, with no baggy space. In particular, look for snug cuffs on arms and ankles; we always look for a wide, comfortable waistband on leggings too.
Style and length
Thermal tops usually have a round crew neck or a high, zipped neck – the latter can double up as a neck warmer, and some tops also sport hoodies for extra warmth around your neck and face. Base layer tops are available with long sleeves or in T-shirt cuts; we usually pick long-sleeved options as they feel comfier worn under mid layers or a waterproof shell. We also look for base layers that use flatlock seams – this avoids any rubbing against your skin.
Materials
Base layers are usually made from either synthetic materials, such as polyester or a polyester blend, or natural materials such as wool and Merino wool. The advantages of polyester are that it’s very light and quick to dry, and that it’s often more affordable. Merino wool (either 100% Merino or a stretchier blend) tends to be pricier, but it’s very soft, long-lasting, naturally antibacterial and can be better at wicking away sweat, so it typically doesn’t need washing so often – perfect if you’re planning an extended camping trip that will take you away from showers and washing machines for a few days.
Wool base layers can be slightly itchy, so they’re definitely worth trying on in person to check before you buy. You may also find that a Merino blend will have more stretch than pure wool. A third, relatively new option, is bamboo clothing – this vegan material is also antibacterial, often wonderfully soft to wear and more eco-friendly to produce than synthetic materials.
Thermals and base layers by numbers
You may see base layers listed with a number, such as 140 or 220. This refers to their weight in grams, and the higher the number, the warmer, but heavier, the base layer will be. For example, a 140g base layer is ideal for spring and fall, while a 220g will do a good job of keeping you warm in winter. If you can afford to, invest in two sets – one lightweight and one heavyweight – and you’ll be sorted year-round.
What to do with your old thermal underwear
Naturally there isn't much demand for second-hand thermal underwear, but you can make yours last longer by doing a few DIY repairs. Don't worry if your work isn't the neatest, nobody will see it.
Once your thermals are well and truly worn out, you still have some options to keep them out of landfill. If you're in the UK, the Waste and Resources Action Program (WRAP) has a postcode search tool that will help you find your nearest textile recycling drop-off point. If you live in the US, Subset (formerly known as Knickey) specializes in taking underwear and socks, which are then turned into things like insulation, carpet padding, and furniture batting. You'll also get a voucher for up to $20 off your next purchase.
