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The saying ‘there’s no bad weather, only bad clothes’ is an unsurprisingly British view, doubtless thanks to the rain, wind and cold that dominates winter in the UK. It also rings very true, and wearing the right clothes can help you feel ready to take on whatever the weather brings.
It all starts with the first layer of clothing you put on and when the temperatures nosedive, thermals are absolutely essential.
Whether you’re wearing them with your favourite gym leggings, some ultra slimming sportswear or just chucking them on under your day to day clothes, the right thermal wear traps warm air as close to your skin as possible and keeps moisture at bay, keeping you dry and toasty while you go about your day.
Thermals that keep me warm while adding as little bulk as possible under my clothes is a priority
I tested a range of thermal wear from specialist brands including M&S, Uniqlo and Intimissimi to find out which thermals are best for everyday wear, as well as the best thermals for sensitive skin and the best thermals for outdoor activities.
Best thermals: Quick list
How we test thermals
As someone who grew up in a tropical climate, it’s of utmost importance that I invest in good quality layer to survive the bitter winters of Britain.
Thermals that keep me warm while adding as little bulk as possible under my clothes is a priority as I dislike the feeling of wearing thick jumpers on top of even more thick fabrics.
I tested thermal tops and leggings of different thicknesses, from gossamer-thin fabrics that are barely registered on the skin, to thick fleecy ones that make the wearer feel like a teddy bear.
However, I also get very hot quickly while walking and hiking, so sweating becomes a concern as it can make you feel cold and damp even while wearing plenty of layers.
So breathability was a feature I preferred, and I tested this by trying out thermal tops and leggings with varying blends of natural and synthetic materials.
I test each piece for breathability and comfort
I wore thermals both indoors and outdoors, testing them under everyday clothes as well as under just a coat to see how efficient they would be at keeping me toasty.
In my assessment of each item of clothing, I determined how they looked underneath my clothes and whether they appeared seamless or bulky.
I also tested each piece for breathability, which I determined based on how much I sweated whilst taking brisk walks in the thermals and whether that sweat was wicked away quickly.
Finally, I took note of how warm the thermal clothing made me upon stepping out of my flat, and after a brisk walk or a day out.
The best thermals to buy right now
1. Best thermals overall: Uniqlo HEATTECH Scoop Neck T-Shirt
HEATTECH Scoop Neck T-Shirt (Long Sleeve)
Uniqlo’s propietary HEATTECH thermalwear technology is at its best in this ultra lightweight, versatile top. The scoop neckline and skintight fit makes it practically invisible under most outfits. It starts working from the moment you put it on, as it absorbs your own body heat to generate warmth and keep you feeling cosy from the get-go.
What we love
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HEATTECH technology works immediatelyStarts absorbing heat from the body and retaining it from the moment it’s put on
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Skin-tight and versatileHugs very close to the body so does not add any bulk under clothing
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Different neckline optionsComes in crew neck and turtleneck versions
Uniqlo’s trademarked HEATTECH thermal wear reigns supreme with its versatility, breathability and performance. It generates warmth from the moment you put it on and continues to do so at a highly efficient rate as you move about and produce more body heat. Even when you are stood still, it retains any heat that has already been built up for an impressively long time. The scoop neck design means it does not peek out from under clothing, but you can also get it in a crew neck and turtleneck version if you prefer.
2. Best thermals for outdoor activities: Peter Storm Womens’ Short-sleeve Thermal Crew Neck T-shirt
Peter Storm Womens’ Short-sleeve Thermal Crew Neck T-shirt
A T-shirt style thermal can be hard to find, but there are some days when a long-sleeve is too toasty and a vest is just not warm enough. This soft, close-fitting T-shirt thermal is the answer.
What we love
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Short sleevesKeeps you warm without being hot
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Can be worn aloneIf you’re doing plenty of physical activity, this is warm enough to wear alone on a milder winter day
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Soft and comfortableGreat for when you need to be flexible
What could be better
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Can add bulkAdds volume under clothes
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Not breathableThe goal is warmth here, but you may find yourself sweating a lot in this polyester-viscose blend
Short-sleeved thermals really do exist, and this one is great for outdoor sports and activities as it keeps you warm, but not too warm. It fits close to the body but is not skin tight, so it does add a little bit of bulk underneath a top, but if you’re out running or hiking anyway, you may find it’s enough to just wear this under a sporty jacket or windbreaker in milder weather. It is soft and comfortable, with a flattering fit.
3. Best fleece thermals: Heatgen Maximum Thermal Fleece Top
Heatgen™ Maximum Thermal Fleece Top
Thick, soft and fleecy for the very coldest of days, this top is made with M&S’s proprietary Heatgen technology keeps you extra warm and snuggly.
If you want to feel like a life-sized teddy bear, this fleecy thermal from M&S is exactly what you need. It’s super warm and cosy, and comes with matching leggings in the same fabric. However, it is thick and adds plenty of bulk underneath clothes, so I would recommend wearing on its own or under a larger jumper and skirts so you don’t feel like the Michelin man. It is supremely comfortable and the mock neck is flattering while protecting your neck from bitter winds. It’s also great for lounging around at home and keeping very warm indoors.
4. Best lightweight thermal: Intimissimi Boat Neck Modal Cashmere Ultralight Jumper
Boat Neck Modal Cashmere Ultralight Jumper
Made with super soft modal fabric, with just a hint of cashmere, this is a highly luxurious feeling jumper that is sheer and makes for a thin, yet warm and comfortable layer under clothes.
What we love
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Soft and airyA highly breathable fabric that feels super soft against bare skin
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A very thin layerPractically invisible under clothes
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Keeps warm in moderately low temperaturesWarm enough for mild winter days
This top is loved on social media, particularly among TikTokers, and for good reason – it is so soft, comfortable and breathable, and feels really good against bare skin. It is mostly made from modal, a semi-synthetic fabric made from the cellulose of beech trees, combined with just a touch of cashmere for a luxurious feel.
It is very thin and sheer, so do be careful as it may catch on long nails or sharp jewellery. It is excellent for moderately low temperatures, but does not perform quite as well in sub-zero temperatures.
5. Best silk thermals: Jasmine Silk Ladies Pure Silk Ivory Thermal Top
Ladies Pure Silk Ivory Thermal Top
Made from 100% mulberry silk, this thermal top is very luxurious. It slips on easily and keeps you warm while maintaining breathability and lightness.
What we love
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Pure silkFeels luxurious while still being an excellent insulating layer
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Thin layerAdds zero bulk under clothes
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Highly breathableWicks sweat away efficiently and is good for sensitive skin
After learning recently that silk is highly insulating – it traps warm air while wicking sweat away from the skin – I found this highly luxurious thermal top that performs really well in the cold. Due to being a natural material, it maintains a high level of breathability, which means sweat doesn’t linger for long, and it keeps the wearer warm over a long period. It holds up in very low temperatures underneath additional layers of a jumper and coat, and is thin enough not to add any bulk underneath. At £50, it certainly is an investment, but one that is worth it if you look after the delicate silk.
6. Best thermal set: Second Skin Thermals
Second Skin Thermal Long Sleeve Top
Pour Moi’s Second Skin thermalwear is made from super soft and smooth fabric that stops heat from escaping, keeping you warm and cosy. The top comes in a variety of colours and matching leggings are available, making it the perfect set to wear at home.
What we love
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Soft and smoothExtremely comfortable, good for sensitive skin
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Stops body heat from escapingKeeps you feeling toasty
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Great for loungingStretchy, not overly tight fitting
What could be better
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Very little natural fibresMade from acrylic, viscose and elastane, which makes it less breathable
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Adds slight bulk under clothesDue to not being skin-tight, it can feel thick under clothes
We found these thermals from lingerie brand Pour Moi to be incredibly soft, smooth and warm, and were particularly comfortable wearing them on a cold day spent indoors as matching leggings are available for £25, making a complete set for lounging.
We loved how comfortable and stretchy the fabric was, as well as how well it fit without being too tight and clingy. It does add a little bit of bulk under clothing, although it isn’t very noticeable – it’s a case of individual preference, but because it isn’t skin tight, wearers may feel like their layers are thicker than they’d like.
7. Best all-weather thermals: Smartwool Women’s Classic All-Season Merino 1/4 Zip Base Layer
SmartwoolWomen’s Classic All-Season Merino 1/4 Zip Base Layer
The fabric in this thermal top is composed mainly of lightweight merino wool, which gives it high breathability while still trapping body heat to keep you warm and dry in any weather.
What we love
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High natural fibre contentMade with 88% merino wool
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Keeps dryWicks sweat away from the skin quickly
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Flexible and comfortableGreat for outdoor physical activities
Available on Go Outdoors, this thermal really impressed us with the natural fibre content – 88% merino wool and 12% nylon, which makes it highly breathable yet warm in any weather. We loved wearing it while hiking as it kept us dry by wicking sweat away from the skin quickly and didn’t become sodden with sweat at any point. Thermals that retain water without drying quickly can leave you feeling even colder, so it’s important the layer keeps you dry. We really liked wearing this outdoors and it was comfortable and flexible enough for physical activity.
Verdict
Uniqlo is an undisputed champion in this area with its HEATTECH thermals, which offer serious warmth without adding any bulk at all underneath clothes. This is really important because wearing too many thick layers can make you feel very uncomfortable or, even worse, overheat. We found that Uniqlo thermals also last a really long time – our tester has thermals from the brand that have lasted over five winters so far and are still in great shape.
But there are also many other great thermals on the market right now. Comfort kings M&S has its own proprietary HEATGEN thermal technology that make the fleeces so warm and cosy you feel like a teddy bear. On the other end of the spectrum, Intimissimi’s cashmere-blend Ultralight range layers are so thin that they are sheer, but they feel incredibly soft against bare skin and do a decent job at keeping you warm on mild winter days.
Pour Moi’s Second Skin range is so comfortable and stretchy, while Jasmine Silk’s silk thermals were a gamechanger
Pour Moi’s Second Skin range is so comfortable and stretchy, we loved them for lounging around at home. For a more luxury thermal, Jasmine Silk’s 100 per cent silk thermals were a gamechanger and while they are expensive, they are highly insulating and the natural fibre content is worth the money.
For the more outdoorsy people among us, Go Outdoors is a great source for thermals that work for active lifestyles, like the Peter Storm T-shirt thermal, which is a rare find, or the Smartwool merino base layer, which is made from an impressive 88 per cent wool.
FAQs
Is it better for thermals to be tight or loose?
Thermals work by trapping a layer of air between the skin and the fabric, which keeps warmth from escaping. This means that thermals should fit close to the skin in order to stop cold air from the surroundings from entering and disrupting this layer.
A snug fit is therefore better when it comes to searching for the right thermal. This allows the garment to wick sweat away from the skin more efficiently too, keeping you dry.
However, they should not be so tight that you feel restricted or claustrophobic, or bunches up in awkward spots like under the arms. Most thermals have some elastane or nylon to allow for stretch, but others that are thicker may offer less flexibility.
What is the best material for thermals?
In the past, winter layers were mainly made from wool and other natural fibres, but nowadays you are more likely to find synthetic blends that may be purely synthetic, or blended with natural fibres.
Acrylic and polyester are popular synthetic materials used in many modern clothes. Whilst these do a really good job of making you warm, they also don’t allow for much breathability – which can make you feel too hot too quickly, and often retains body odour so you have to wash them often.
Natural fibres like wool, cotton, linen, and silk allow much more breathability, which helps your body regulate temperature better. They also do not require as much cleaning, as simply airing out the garments can reduce odour and keep them feeling fresh for longer.
However, it is harder and more expensive to find thermals made from 100 per cent natural materials, and blends with synthetic or semi-synthetic (like viscose and modal) are much more common and can offer both breathability and warmth.
