The best thermal underwear for layering like a pro

Brrrrr. Feeling the cold? Or maybe you have an icy holiday on the horizon?

Either way, some good thermal underwear will help sort you out.

From merino woolbase layers to polyester blend tights, we’ve hand-picked the best thermal underwear options available this season. 

Read on for the lowdown on layering.

The best thermal underwear for women

Best thermal underwear overall The best thermal underwear for seriously cold climatesBest budget thermal underwear for womenBest lightweight thermal underwear 

The best thermal wear for layering this season 

When it comes to shopping for the best thermal underwear, we’re all about options that are practical, price worthy and provide the warmest base layer possible. 

So, rest assured, each of the selections below has been carefully chosen with these factors in mind. 

Best thermal underwear overall

Photo: Go Outdoors

Smartwool Women's Classic Thermal Merino Base Layer

Crafted from 100 percent merino 250 wool, this thermoregulating base layer from Smartwool offers superior warmth and comfort.

Breathable and moisture-wicking, with flatlock seams to minimise the likelihood of chafing, this odour-resistant shirt is perfect for winter activities and daily layering. 

Plus, thanks to its slim fit and flattering cut, it works well as a standalone option, too.

Available in an array of colours from a variety of quality retailers, you can even shop a variation that uses plant dyes to produce the colourways.

Make it a set: Enjoy the same superior merino experience with a pair of Smartwool's best thermal long johns.

The best thermal underwear for seriously cold climates

Photo: Icebreaker

Icebreaker MerinoFine Long Sleeve Roll Neck Thermal Top

Heading to the mountains or super snowy climates and in desperate need of wrapping up warm?

Look no further than Icebreaker’s merino range.

It may not be cheap, but it’s effective.

Made from 15.5-micron merino wool fibres, this is one seriously soft, comfortable base layer — and the high neck is perfect for keeping your neck protected and your body heat cocooned. 

We’re also major fans of the drop hem and extra-long sleeves with thumb holes. There’s nothing worse than icy wind creeping up your back and sleeves, and these nifty touches prevent that. 

Make it a set: Shop your ultra-warm matching thermal pants here.

Best budget thermal underwear for women

Photo: Uniqlo

HEATTECH Crew Neck Long Sleeved Thermal Top

Just because it’s cheap doesn’t mean it’s unreliable. 

Uniqlo consistently comes out on top when it comes to quality thermal wear that looks as good as it feels — without breaking the bank.

Available in a range of colours, these tops offer extra warmth and a flattering fit that’s so stylish you won’t want to hide it.

Best lightweight thermal underwear 

Photo: Ellis Brigham

Artilect Boulder 125 Women's Long Sleeve Crew

There’s nothing worse when you’re trying to keep warm, than bulky garments that don’t lend themselves to layering. 

That’s why we love this Artilect Long Sleeve Crew. 

Crafted from ultralight Nuyarn 125 merino wool, which offers even more warmth than traditional merino, this shirt also boasts breathable mesh underarm panels for added comfort, and its crew neck design makes it easy to wear beneath other garments.

Best sweat-wicking thermal underwear

Photo: Under Armour

Women's ColdGear® Authentics Crew

Known the world over for its top-quality sportswear, it stands to reason that Under Armour would feature in our round-up of the best thermal underwear in the UK.

This Authentics Crew shirt has been specially designed with an extra warm, brushed interior and fast-drying exterior, doesn’t ride up as you move and even includes mesh ventilation panels beneath the underarms — so you’ll stay fresh and dry even in the sweatiest of situations. 

Make it a set: Looking for your new go-to exercise gear? Why not shop the same sweat-wicking matching bottoms too? 

Best thermal underwear for novelty lovers

Photo: Sweaty Betty

Graphic Novelty Base Layer Top

You save £21.25 (25%)£85

Who said base layers were boring? 

We’re obsessed with this statement thermal top from Sweaty Betty.

Made from a soft-touch antibacterial knit and sweat-wicking technology this retro-style thermal is so cute you won’t want to cover them up.

Body, sorted. Now, what about actual thermal underwear?

Okay, so we’ve covered the obvious. Your arms, torso and legs will be kept toasty warm, no matter the climate. But what about your ‘bits’? 

Feel like you need a little extra coverage and insulation across your key areas? 

Well, there are thermal bras, knickers and tank tops that will do the trick! We’ve carefully selected our favourite options for you below.

For upper body layering

Photo: Alpine Trek

Women's Siren Cami – Merino base layer

You save £7.49 (14.99%)£49.95

Anyone who feels the cold knows an effective tank top is worth its weight in gold.

And this Siren Cami longline tank is a winner.

Made from mulesing-free wool, the length of this tank keeps your kidneys and lower back warm, whilst the ultra-soft merino regulates your body temperature. 

Available in three colours, ranging in size from XS to 3XL. 

For keeping your besties warm

Photo: Icebreaker

Women's Merino Queens Clasp Bra

You save £25 (50%)£50

Merino and wool bras might seem excessive, but they’re actually a game-changer. 

Not only do they keep your best buds toasty warm in chilly conditions (therefore combating the ‘nip-through-shirt’ scenario), but they’re also great for keeping cleavage and ‘underboob’ dry when exercising in colder climates.

Complete this stylish and super cosy set by adding the high-cut briefs to your bag.

For keeping your butt cosy

Photo: Alpine Trek

JOHA Women's Hipsters 70/30 – Merino base layer

You save £3.14 (14.99%)£20.95

Why bother with merino undies, you may ask.

Well, aside from keeping your bits warm and protected from the elements, merino is also a super breathable fabric and these lightweight knickers are fast-drying and odour-resistant to boot.  

These key factors make them a great option for anyone embarking on hikes, treks, long-haul travels — or even partaking in winter sports or gym activities. 

Made from 30 percent silk and 70 percent merino, these hipster-cut underwear for women are available in sizes XS-XXL in both forest green and black.

For keeping your toes toasty

Photo: Heat Holders

Ladies Twist Socks

Known for producing the cosiest socks, Heat Holders have come up trumps once again when it comes to quality women’s thermal socks.

These superthick socks provide ample layering and cushioning for even the coldest feet. You’ll wear them all winter long, we promise.

How to choose the best base layers

As with choosing any clothing, everyone will have slightly different preferences when it comes to selecting their favourite thermals. 

That said, there are a couple of key elements to consider when making your choices:

• Where will you be wearing the thermals? Your needs (and levels of warmth required) will be different depending on whether you plan to wear them around town under your regular clothes, or under ski pants on a snowy mountain.

• How much are you willing to spend? While it’s possible to find great base layers for affordable prices, if you want layering crafted from natural fabrics with sweat-wicking properties and four-way stretch, you may need to invest a little more moolah. 

• Remove the restriction. Since, by definition, you’ll usually be wearing your base layers under other items of clothing and partaking in an array of activities whether skiing, snowboarding, slothing on the couch or even stretching in a yoga class, you want to be able to move freely and with a good range of motion. So opt for garments with comfortable waistbands and a decent amount of stretch

• Are you looking to make a statement? Traditional thermals tend to be more on the plain side, with merino wool options often coming in muted, neutral colours. That said, as thermal wear increases in popularity, more young, hip and vibrant brands are creating options that are patterned and loud — often with higher price points to match. 

Photo: Winfield Outdoors

What is the best material for thermal underwear to be made of?

Merino wool is the most popular fabric for effective base layers. 

Why?

According to Winsfields Outdoor, an expert outdoor retailer, merino tends to be the fabric of choice for a few reasons:

• It’s the most naturally warm base layer fabric

• It regulates your body temperature, making it great for outdoor activities like hiking and skiing 

• It’s naturally antibacterial, so your body odour will not stick to the fabric 

While merino may be considered the best fabric for warm base layers, synthetic fabrics may be preferable if you require more of a compression base layer for sports — or are on a more limited budget. 

Photo: Winfields Outdoor

Should my thermals be tight or loose?

Though most people opt for a tighter fit for base layers — so that they fit beneath outer layers and trap body heat in the process — there is a slight difference between the fit for synthetic versus merino thermals.

Winfields Outdoor states, ‘synthetics should feel tight against your skin while providing you with plenty of flexibility to move.

‘Merino wool can be looser than a synthetic fabric and should be comfortable next to the skin rather than tight on it. Think of them as more of an ‘athletic’ or ‘fitted’ body fit than being skin-tight.’

Photo: Winfields Outdoor

Which of these thermal underwear options is for you?

Feeling warmer just thinking about these delicious merino thermals?

It’s time to make your dream a reality.

Enjoy excellent warmth and comfort in a Smartwool Women's Classic Thermal Merino Base Layer, perfect for both everyday layering and enjoying winter activities.

For the perfect lightweight base layer, you can’t go wrong with the Artilect Boulder 125 Women's Long Sleeve Crew. As a superfine merino shirt with increased durability and warmth — it’s a no-brainer as our pick for the best lightweight layering option.

And when it comes to keeping your bits toasty, we strongly recommend investing in a pair of Joha's Women's Hipsters, while your toes will thank you for stocking up on some Ladies Twist Socks.