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Best thermal underwear and base layers for women to keep you warm this winter

Layer up to fight the freeze with our pick of the best women's thermal underwear and base layers, all recommended by Mumsnet users, the largest online network of UK parents.

By Lucy Cotterill | Last updated Dec 6, 2022

Woman wearing thermal underwear

There’s nothing worse than feeling too cold when you’re out and about, and a layer of thermals under your clothes can easily make the difference between a comfortable winter walk and a freezing, miserable trudge. What’s more, today’s high-tech thermal fabrics are thin and versatile enough to blend in with the rest of your wardrobe, making them excellent winter staples as well as underwear. 

Thermals aren’t just for outdoor wear, however. Amid a cost of living crisis, many of us are seeking alternative ways to keep warm when working from home this winter, seeking out heat-generating base layers to help layer up and prevent the need to turn up that thermostat (why not team up with one of the best blanket hoodies for an ideal way to stay toasty without sending costs spiraling). Thermal underwear works to conserve body heat while regulating your temperature so you don’t get sweaty and uncomfortable. A must for skiing or hiking in cold climates, thermals can also make day-to-day life that bit more cosy during the winter months. 

Whether you’re shopping for discreet everyday layers, budget-friendly thermals for working from home or super-insulating skiing and adventure gear, the Mumsnet community have you covered. We’ve gathered the wisdom of the largest online network of UK parents to bring you our pick of tops, leggings and base layers. 

Plus, if you're looking for more solutions to keep warm as temperatures plummet, we've been hunting down the top buys to stay snug this year. Don't miss our round-ups of the best blanket hoodies for kids, best winter coats for women, best weighted blankets for kids, and best draught excluders – all of which have been carefully researched and selected to ensure we're only bringing you the very best. 

Here are the best women’s base layers and thermals to buy in 2022.

1. Best overall thermal underwear: Uniqlo Heattech Scoop Neck Long Sleeved Thermal Top

Uniqlo Heattech thermal underwear

Price on writing: £14.90 | Buy now from Uniqlo

Key specs

Material: 38% Polyester, 30% Acrylic, 20% Viscose, 12% Elastane | Colours: Dark brown, white, black, pink, beige and brown | Sizes available: XXS to XXL

Reasons to buy

  • Choice of colours available 
  • Soft, stretchy and comfortable 
  • A low neckline can easily be worn under other clothing

Reasons to avoid

  • Not all sizes are available 

What Mumsnet users say

“Uniqlo Heattech can't be beaten IMO”  (Tried and tested by Mumsnet user helenabonhamfarter)

“Uniqlo. I live in them in the winter. The best value for money versus warmth I've found. Plus they are usually nice enough looking that you can just wear them alone too. I have the thinnest ones and the thickest ones and love them all.” (Recommended by Mumsnetter alpinia

Our verdict

Our favourite features? When it comes to reliable and effective base layers, Mumsnet users couldn’t speak more highly of the Uniqlo Heattech range, which is not only available in a range of colours and styles but comes with an affordable price tag too. 

Lightweight enough to wear under everyday clothes, yet warm enough to really feel the difference, it’s no wonder they’re so popular. This long-sleeved scooped neck top is versatile enough to wear on its own, but thanks to its low neckline, is also ideal for  layering under a jumper or shirt for the ultimate cosiness. 

Made from a polyester and acrylic mix, the fabric is soft, stretchy and moisture wicking, whilst also being supremely comfortable. Thanks to the quick-drying material, it’ll soon become an essential for your winter wardrobe.

Team up with one of the best heated throw blankets for extra cosiness. 

2. Best budget thermal underwear: Sainsbury’s TU Heat Active Black Medium Warmth Thermal Top

Sainsbury’s TU Heat Active Black Medium Warmth Thermal Top

Price: £12 | Buy now from Tu

Key specs

Material: 56% Acrylic, 37% Viscose, 7% Elastane | Colours: Black (other designs available) | Sizes available: UK sizes 8 - 22 

Reasons to buy

  • Wide range of thermal products in the Heat Active range
  • Fitted design
  • Lightweight enough to layer 

Reasons to avoid

  • Other colours are slightly more expensive 

What Mumsnet users say

“I’ve found Sainsbury’s thermals very good & Sainsbury’s/Tu (also at Argos) have frequent 20% off sales.”  (Tried and tested by Mumsnet user Cat3i)

“I bought two from Sainsbury’s about five years ago and have worn them through every winter since. Brilliant quality” (Recommended by Mumsnetter FourChimneys

Our verdict 

Our favourite features? This super soft long-sleeved Heat Active top comes with a medium warmth rating, designed to ‘bounce back’ your natural body heat and keep it close to your skin.

If you need to pick up on some thermal base layers but are limited on budget, the Heat Active range from Sainsbury’s is a great place to start. 

Longsleeved and lightweight, with a flattering fitted shape, the crew neckline on this top makes it ideal for wearing alone, whilst also being discreet enough to layer under your winter woollies on particularly chilly days. Team up with one of the best heated gilets to help stay extra warm when out and about this winter.

3. Best thermal leggings: John Lewis Heat Generating Thermal Leggings

John Lewis Heat Generating Thermal Leggings

Price: £16 | Buy now from John Lewis

Key specs

Material: 57% acrylic, 39% viscose, 4% elastane | Colours: Black | Sizes available: UK sizes 8 - 18

Reasons to buy

  • Snug, fitted design 
  • Matte finish
  • Heat generating 

Reasons to avoid

  • Sizing is in bundles (8-10,12-14, 16-18) so getting the sizing right can be a bit of trial and error. 

What Mumsnet users say

Currently very snug in heat-generating leggings from John Lewis.”  (Tried and tested by Mumsnet user Jocasta2018)

Our verdict 

Our favourite features? With a snug yet comfortable fit and a non-shiny matte finish; they look super stylish teamed up with a big fluffy jumper and boots and the comfortable waistband means they won’t slip down.

Do you find your legs feeling chilly in winter but feel uncomfortable and restricted wearing fitted trousers or jeans? 

These thermal leggings from John Lewis are a great alternative to trousers and they can not only retain your body heat but actually help generate it too, using the moisture from your skin. 

Moisture-wicking and anti-static, you’ll stay cosy yet comfortable even on more active days. Why not team up with one of the best winter coats for women to keep you extra toasty while out and about.

4. Best thermal base layer: Marks and Spencer Heatgen Thermal Long Sleeved Top

Marks and Spencer Heatgen Thermal Long Sleeved Top

Price: £25 for two | Buy now from Marks and Spencer 

Key specs

Material: 66% acrylic, 28% viscose and 6% elastane | Colours: Choice of five colour packs including Black, Cream, Red, Raspberry and Navy | Sizes available: UK size 6 - 22

Reasons to buy

  • Heat retaining base layer
  • Soft and stretchy fit 
  • Lightweight enough for layering

Reasons to avoid

  • All the colour options (except one) are quite dark

What Mumsnet users say

“I love the M&S ones. I get more use out of the Heatgen as opposed to Heatgen Plus version though. They’re too warm to layer and the seams are quite thick for my liking. Would like to see some more muted mid-tone colours.”  (Tried and tested by Mumsnet user Coralolive)

“I have two M&S ones (black sparkle and leopard print) and they are brilliant. You would be able to wear them under dungarees, but not on their own with a jacket or undone cardigan because they are quite sheer/thin.” (Recommended by Mumsnet user MermaidMeemaw

Our verdict 

Our favourite features? Snug yet stretchy, the Heatgen fabric retains heat from your body whilst feeling super soft against your skin.

When there’s an unpleasant chill in the air, a thermal top layered under your usual clothes can help trap heat and keep you warm and comfortable. 

These lightweight Heatgen Thermal Tops from M&S come with long sleeves and an attractive scooped neckline that makes a perfect base layer. 

They wash well at 40°C and dry quickly, but thanks to the handy two-pack, you can have a constant cycle and won’t get cold when one’s in the wash. If you prefer a thicker design, M&S also offer similar tops in the Heatgen Plus range, even warmer for when the temperatures drop below zero. 

Check out our guide to the best hot water bottles for more ways to stay warm while the temperatures plummet this winter.

5. Best merino wool thermal underwear: Mountain Warehouse Merino Women’s Pants

Mountain Warehouse Merino Women’s Pants

Price on writing: £24.99 | Buy now from Amazon

Key specs

Material: Merino Wool 80%, Polyester 20% | Colours: Three - black, grey and red | Sizes available: UK sizes 4 - 28

Reasons to buy

  • High-performance merino wool
  • Super soft and comfortable
  • Lightweight and breathable 

Reasons to avoid

  • More expensive than some

What Mumsnet users say

“Mountain Warehouse does some nice merino ones with a comfortable wide waistband”  (Tried and tested by Mumsnet user BrownTableMat)

“Mountain Warehouse merino wool ones are lovely.” (Recommended by Mumsnetter SummaLuvin

Our verdict 

Our favourite features? The elastic waistband ensures they’ll stay put even when you’re at your most active, whilst the lightweight material makes them easy to store and quick drying when washed.

For seriously toasty thermals, merino wool is certainly the best choice of fabric, providing warmth and protecting you from the elements without feeling bulky or making you sweaty and overheated. 

These Merino Women’s Pants are made from naturally breathable high-quality wool to keep you warm and comfortable in all conditions, making them a practical choice for winter walks, hikes or everyday wear. (Complete the look with our guide to the best walking boots.) 

6. Best silk thermal underwear: Patra Women’s Silk Blend Long Johns

Patra Women’s Silk Blend Long Johns

Price: £39 | Buy now from Patra

Key specs

Material: Spun Silk 10% - Modal 90% | Colours: Two - black or cream | Sizes available: XS to 2XL

Reasons to buy

  • Naturally soft and luxurious
  • Ideal base layer for cold weather
  • Modal fabrics increase durability 

Reasons to avoid

  • Hand wash or gentle 30-degree wash recommended
  • Limited to two colour choices 

What Mumsnet users say

“Patra silk thermals are the best!” (Recommended by Mumsnet user FreyaMountstuart)

“Patra silk, great leggings and wonderful thermal vests” (Tried and tested by Mumsnet user FelicityFlops)

Our verdict 

Our favourite features? These Patra silk blend long johns combine the comfort of silk with the durability of modal to create a resilient yet luxurious base layer for chilly weather or outdoor adventures. 

If you’re looking for thermals that can keep you warm whilst still feeling soft and luxurious, silk or silk blend thermals make a great choice for layering this winter and are kind and gentle on sensitive skin.

Naturally soft with double-layered cuffs to ensure a good fit, these long-john thermals not only look great but are easy to care for and maintain their shape after washing.

7. Best extra warm thermal underwear: Icebreaker Women’s Merino 175 Everyday Long Sleeve Crewe Thermal Top

Icebreaker Women’s Merino 175 Everyday Long Sleeve Crewe Thermal Top

Price on writing: From £52.44 - £88.52 | Buy now from Amazon

Key specs

Material: 100% Merino Wool | Colours: Three - black, red or khaki | Sizes available: XS to XL

Reasons to buy

  • Available in a choice of thicknesses for all weather conditions
  • Made from high-performance merino wool
  • Moisture wicking to prevent sweating or overheating

Reasons to avoid

  • Costly

What Mumsnet users say

“Icebreaker - New Zealand merino wool. They are amazing. I use their thick and thinner-weight round neck tops and the same again with their quarter zip tops for running in winter. Plus their neck warmer - I must wear that 6 months of the year!”  (Tried and tested by Mumsnet user MetricMs)

“Seconding Icebreaker - wash and wear well and so warm.” (Recommended by Mumsnetter Martinisarebetterdirty

Our verdict 

Our favourite features? The stretchy slim fit is flattering on all body shapes, whilst the crew neck can easily become a non-visible layer under jumpers and sweats. 

Mumsnet users couldn’t speak more highly of Icebreaker thermals, which offer high-quality merino wool fabrics and are available in a range of thicknesses to suit every type of weather condition. The number 175 refers to the weight of the wool - in this case, lightweight - but Icebreaker offers up to 380 for freezing or icy conditions. 

This all-purpose base layer top is made from a breathable 100% merino wool which feels super soft to the touch. The high-performance fabric is moisture-wicking - helping regulate body temperature in all weather conditions and prevent sweating or odours. 

8. Best lightweight thermal underwear: Rohan Women’s Merino Union 150 Crew

Rohan Women’s Merino Union 150 Crew

Price on writing: £55 | Buy now from Rohan 

Key specs

Material: 63% Merino Wool 37% Polyester | Colours: Dark charcoal | Sizes available: S to XL

Reasons to buy

  • Soft merino wool
  • Breathable and moisture wicking
  • Flat-locked seams are not visible when layering 

Reasons to avoid

  • Costly
  • Only one colour choice 

What Mumsnet users say

“Rohan base layers are thin but really warm. I wear the men's Alpha silver tee. They are very fine for layering, dry overnight and unbelievably warm. I have Iceland tops but much prefer the Rohan one. I'm a 14/16 and the men's medium is perfect.”  (Brand recommended by Mumsnet user supperlover)

Our verdict 

Our favourite features? Made from superfine merino wool and polyester, this 150 crew base layer is soft and comfortable against the skin, whilst being durable and hardwearing for colder temperatures.  

If you’ve previously found thermals too bulky or found that thicker seams are visible when layered under your clothes, the Rohan 150 Crew is a fab alternative. 

Unlike some other thermal designs, the seams on this top are flat locked to prevent bulking or riding up under your clothes. It can easily be worn alone, or under thicker jumpers or fleeces to trap heat and maintain warmth on colder days.

9. Best moisture-wicking thermal trousers: ACAI Thermal Skinny Outdoor Trousers

ACAI Thermal Skinny Outdoor Trousers

Price: £99 | Buy now from ACAI Outdoors 

Key specs

Material: 91% polyester, 9% Spandex | Colours: Five - Black, deep navy, graphite, aubergine, forest green | Sizes available: UK sizes 6 - 22

Reasons to buy

  • Water-resistant 
  • Fleece lined for comfort
  • Moisture wicking to prevent sweat and odour 
  • Stylish design in a choice of colour 

Reasons to avoid

  • An investment due to the high price point

What Mumsnet users say

“I have the thermal skinny outdoors ones and love them. Really comfortable and they look smart.”  (Tried and tested by Mumsnet user toomuchlikemyusername)

“I have 2 pairs of the thermal ones and wearing them daily...not for exercise but so I can work from home without heating the entire house all day 😁 for my daily but sedentary use they are brilliant, although I have also worn them in the garden and been kept lovely and toasty” (Recommended by Mumsnet user AmIAWeed

Our verdict 

Our favourite features? Breathable and moisture-wicking, you can easily get your steps in without becoming sweaty, whilst the secure zipped pocket can safely stash your phone or keys whilst you explore your surroundings.

If you like to spend your winter days out on walks or hikes with your family or friends, you’re going to need some high-performance trousers that can keep you warm and dry while preventing overheating. 

These ACAI Thermal Skinny Outdoor Trousers are made by women for women and combine high-performance outdoor fabrics with a modern and stylish design. 

With a soft, comfortable and flattering fit, these fleece-lined trousers are made from a stretchy soft shell which is durable and shower resistant. They dry in minutes, so even an unexpected downpour won’t stop you from enjoying your day. 

10. Best thermal socks: Heat Holders Ladies Extra Soft Fluffy Non-Slip Thermal Low Cut Ankle Slipper Lounge Bed Socks with Grips

Heat Holders thermal socks

Price on writing: From £10.99 - £14.99 | Buy now from Amazon

Key specs

Material: 58% Acrylic, 36% Polyester, 5% Nylon, 1% Elastane | Colours: Over 20 colour styles | Sizes available: 4-8 UK (One size)

Reasons to buy

  • Heat retaining materials 
  • Soft and cosy yet less restrictive than slippers 
  • Choice of designs 

Reasons to avoid

  • Too bulky to wear under shoes 
  • More suited to indoor use 

What Mumsnet users say

“I have loads of pairs of Heat Holders. They are great”  (Tried and tested by Mumsnet user SunbathingDragon)

“Another vote for Heat Holders here. Although I just wear them around the house. Almost like slippers. They are too thick to wear in shoes though.” (Recommended by Mumsnetter Elephant75

Our verdict 

Our favourite features? A pair of thermal socks will ensure your feet are just as warm as the rest of your body, and when it came to toasty toes, Heat Holders come highly recommended by Mumsnet users.

There is nothing worse than having chilly feet, especially when working from home. 

Whilst they may be thick to wear with shoes or boots, (and the non-slip sole grips put them firmly in the slipper socks category) they are perfect for preventing icy toes all winter round, with a thermal tog rating of 2.3. 

How does thermal underwear work?

Thermal underwear uses premium close-fitting fabrics to keep you warm by trapping air close to your skin, so heat loss from your body is minimised. At the same time, they draw sweat away from your skin, doubling their warming effect. When worn under regular clothes, thermal underwear becomes an effective base layer that can keep your body warm and comfortable, whatever the weather.

Do you wear normal underwear underneath thermal underwear?

Yes, whilst the name can be somewhat confusing, thermal underwear is designed to be worn on top of your regular underwear, and more of a second layer of underwear or base layer before putting on your regular clothes. 

How tight should thermal underwear be?

Wear your thermals so they fit snugly, but not uncomfortably so. Most thermal underwear is made from soft and stretchy fabrics, so whilst they may be quite fitted, they should still be comfortable and non-restrictive. You don’t need to size up or down, but instead, opt for your usual dress size.

What is the best fabric for thermal underwear?

Whilst you can easily pick up some affordable and effective thermals made from other fabrics, such as acrylic or polyester blend, Merino wool is by far the warmest and most effective material for thermal underwear, particularly if you are going to be active.

That said, it doesn’t come cheap. If you intend to spend your winter walking or hiking in the great outdoors, they may well be worth the investment, however, to keep warm and toasty when working from home, a cheaper alternative may be perfectly adequate for your needs.

How to choose the best thermals

Here are some things to consider when choosing the right thermals for you:

  • Where will you be wearing them? - Are you looking for some thermal underwear to keep you warm and comfortable when working from home, for winter walks or for more intense outdoor adventures? The best fabrics and ultimately the amount you may need to spend will depend upon your activity levels and what features you require from your thermals.
  • How warm are they? - Some thermals offer a lightweight base layer to wear under your other clothes, whilst some are thicker, warmer or even heat-generating. Consider the environment and the temperatures you will be exposed to, as this may determine the choice of product.
  • Style and cut - Are you looking to wear thermal underwear as a discreet extra layer under your clothes? Some fabrics and cuts are better suited to layering, including those with a scooped neckline and flat seams. Others are thick enough to be worn on their own but may appear bulky or become restrictive when worn with other garments.
  • What material are they made from? - As mentioned above, merino wool is the best fabric for thermals when it comes to comfort and warmth. That said, there are plenty of cheaper alternatives suitable for everyday use.
  • Cost - How much do you wish to spend? As a simple way to keep warm without turning up the central heating, you can pick up thermal underwear with a relatively low price tag. For more high-performance fabrics and features that are well suited to the great outdoors, you may need to spend a little more. 

What brands offer the best women’s thermal underwear?

Uniqlo, Sainsbury’s, M&S and John Lewis are affordable options ideal for more sedate activities such as keeping warm at home or during family walks.

For more extreme weather conditions, the merino wool options from Mountain Warehouse and Icebreaker and water-resistant ACAI thermal trousers offer a more breathable yet hardwearing alternative. 

What’s the best thermal underwear to buy?

The verdict was fairly unanimous amongst Mumsnetters - Uniqlo’s HeatTech range is the best thermal underwear you can buy today, thanks to its combination of warmth, style and value for money. 

How we chose our recommendations

Recommendations from real Mumsnet users 

Mumsnet users have been sharing lots of ideas on how to keep warm during winter. 

First, we sought out the trusted opinions of Mumsnet users, to get their feedback on their favourite thermal underwear including the thermals that they have used themselves and would recommend to others.

We also looked out for any negative reviews, where Mumsetters highlighted products that they felt were poor quality, didn’t wash well, were uncomfortable or simply failed to keep them warm.

Authentic consumer reviews

Finally, to bring you our definitive list of the best thermal underwear, we thoroughly investigated genuine, in-depth customer reviews on retailer sites such as Amazon, Marks and Spencers and John Lewis to get wider consumer experiences regarding the products on our shortlist.

Why you should trust us

We work hard to provide honest and independent advice you can trust and we spend hours scouring the Mumsnet forums and online bestseller lists to find products that real parents rate.

Transparency is really important to us and that's why we're always upfront about where we find our recommendations. We write about products that we feel offer the best value to most parents – the ones that our users would recommend to their own friends and family.