Thermal underwear is a close-fitting base layer that traps warm air next to your skin under clothes or workwear.
Prices checked on Amazon UK, 27 October 2026.
Thermal underwear is a close-fitting base layer that traps warm air next to your skin under clothes or workwear. Sets usually mean a long-sleeve top and long johns; some packs are tops or bottoms only. They suit cold UK winters, outdoor work, skiing prep and chilly houses. This guide compares men's and women's thermal underwear on pack contents, fabric, warmth claims and care from each Amazon UK listing. Clothing prices can differ by size and colour, so the table shows which size we priced. We found 8 thermal underwear sets in stock on Amazon UK with a live buy-box price when we checked on 27 October 2026. Our overall pick is the Gaffer Mens Thermals Top and Bottom Set at £14.99, the budget pick is the Heatwave Women Thermal Underwear Set at £7.95, and our pick for women is the SIMIYA Women's Thermal Underwear at £16.99. Prices and stock change often, so check both on Amazon before you buy.
Quick comparison
| Product | Price | Best for | Size priced | What is included | Fabric (listing) | Warmth claim (listing) | Care |
|---|---|---|---|---|---|---|---|
| Gaffer Mens Thermals Top and Bottom Set | £14.99 | Men's full set | M | Top and long johns | 50% cotton, 50% polyester | Soft brushed inner (listing) | Machine wash |
| Heatwave Women Thermal Underwear Set | £7.95 | Lowest price, women | UK 10-12 | Top and bottoms | 100% cotton (black/white) | Retains body heat (listing) | Machine wash |
| SIMIYA Women's Thermal Underwear | £16.99 | Women, stretch fleece | S | Set (listing) | 95% polyester, 5% elastane | Windproof warm (listing) | Machine wash |
| Heatwave Pack of 2 Men's Thermal Trousers | £9.95 | Men, bottoms 2-pack | L | 2 x long johns | 50% polyester, 50% cotton | 0.45 TOG (listing) | Machine wash |
| Heatwave Pack of 2 Men's Thermal Long Sleeve Tops | £11.95 | Men, tops 2-pack | M | 2 x long sleeve tops | 60% cotton, 40% polyester | 0.45 TOG (listing) | Machine wash |
| Undercover 2 Pack Women’s Pointelle Thermal Top | £14.99 | Women, TOG stated | M | 2 x tops (style on listing) | 65% polyester, 35% viscose | 0.75 TOG (listing) | Machine wash |
| MOBIUSPHY Mens Thermal Underwear Set | £14.99 | Men's active set | M | Top and long johns | Polyester | Lightweight warm (listing) | Machine wash |
| CL convallaria Men's Fleece Lined Thermal Set | £22.99 | Men, fleece lined | L | Top and long johns | 90% polyester, 10% spandex | Fleece lined, windproof (listing) | Machine wash |
Specs from each Amazon UK listing (– = not stated on the listing); prices checked on Amazon UK on 27 October 2026.
Our picks
Gaffer Mens Thermals Top and Bottom Set
Gaffer Mens Thermals Top and Bottom Set
£14.99
Best overall
Heatwave Women Thermal Underwear Set
Heatwave Women Thermal Underwear Set
£7.95
Best budget
SIMIYA Women's Thermal Underwear
SIMIYA Women's Thermal Underwear
£16.99
Best for families
How we pick
We shortlist products sold on Amazon UK using capacity, features, customer ratings and price band. We do not lab-test every model unless a page says so. The Amazon page is the live price. How we recommend.
Compare at a glance
| Product | Last Amazon price | Buy |
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£14.99
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£7.95
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£16.99
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£9.95
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£11.95
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£14.99
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£14.99
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£22.99
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The products
Buying advice
Our top picks
Best overall: Gaffer Mens Thermals Top and Bottom Set (£14.99). A full men's set with thermal top and long johns. The listing says 50% cotton and 50% polyester with a soft brushed inner. Priced for medium in charcoal (2 x full set option on the listing).
Best budget: Heatwave Women Thermal Underwear Set (£7.95). The cheapest full women's set here. Long-sleeve top and bottoms in ultra-soft cotton (black/white 100% cotton on the listing). Priced for UK 10-12 in black.
Best for women: SIMIYA Women's Thermal Underwear (£16.99). A women's fleece-feel set in 95% polyester and 5% elastane. The listing highlights windproof warmth and moisture wicking. Priced for small in grey.
Other thermal underwear worth a look
Heatwave Pack of 2 Men's Thermal Trousers (£9.95). Two pairs of men's long johns with a stated 0.45 TOG rating. 50% polyester and 50% cotton. Useful if you already have thermal tops. Priced for large in black.
Heatwave Pack of 2 Men's Thermal Long Sleeve Tops (£11.95). Matching pack of two men's long-sleeve thermal tops with 0.45 TOG rating. 60% cotton and 40% polyester. Priced for medium in black.
Undercover 2 Pack Women’s Pointelle Thermal Top (£14.99). Women's pointelle thermal tops with a 0.75 TOG rating and brushed inside. Listing offers several top styles; this price is for the long-sleeve option in white, medium, sold as a 2-pack.
MOBIUSPHY Mens Thermal Underwear Set (£14.99). A men's top and long johns set in polyester. The listing describes lightweight warmth, breathability and quick-dry fabric for active wear. Priced for medium in black.
CL convallaria Men's Fleece Lined Thermal Set (£22.99). A midweight (200 g/m²) men's fleece-lined base layer for sport, ski and hunting use on the listing. 90% polyester and 10% spandex with four-way stretch. Priced for large, crew neck black.
Sets vs separate tops and bottoms
A full set is simplest if you need both layers. Heatwave also sells tops and bottoms in 2-packs (£11.95, £9.95) if you want spares of one piece. Check whether the listing is a set or tops/bottoms only before you buy.
Clothing prices on Amazon can change with size and colour, so the price here is for the size shown in the table.
TOG ratings and fabric
Only some brands quote TOG. Heatwave lists 0.45 TOG on the men's packs; Undercover lists 0.75 TOG on the women's pointelle tops. Cotton blends feel familiar; polyester fleece blends are often warmer for outdoor sport.
Thermal underwear should be snug so the warm air stays next to your skin, but not so tight it restricts movement.
What to look for in thermal underwear
Fit. Close-fitting works best; check the size chart for UK or letter sizes.
Fabric. Cotton blends for everyday wear; polyester fleece for outdoor sport and moisture wicking.
Set or separates. Full sets cover top and bottom; 2-packs of tops or bottoms suit replacing one piece.
TOG or warmth claim. Use a stated TOG when you want a clear figure; otherwise read brushed or fleece-lined wording.
Care. Most here are machine washable; follow the listing.
Use. Everyday under jeans differs from ski or work base layers.
How we chose these picks
We only included products that were in stock on Amazon UK with a single live buy-box price in pounds when we checked on 27 October 2026, read with a UK delivery address. We skipped listings showing low stock, no stock line or unclear details, and we avoided repeating products already featured in our other guides. Specs in the comparison table come from each product's Amazon UK listing, and a dash means the listing does not state that detail. Descriptions are based on what each listing says; we have not tested these products ourselves, and we have not used star ratings or review counts.
Prices were checked on Amazon UK on 27 October 2026 and can change at any time. Check the current price, details and delivery date on Amazon before you order.
Frequently asked questions
Are thermal underwear supposed to be tight?
They should sit close to the skin so warm air stays in the layer, but they should not cut off circulation. Use the size chart on each listing; stretch fabrics in this guide are designed to move with you.
Is thermal underwear cotton?
Some is. Heatwave women's sets list 100% cotton on black and white colourways, and several men's packs are cotton-polyester blends. Others are mostly polyester fleece for outdoor use. Check the fabric column in this guide.
Does thermal underwear work?
Yes as a base layer under clothes in cold weather. Warmth depends on fabric, fit and what you wear over it. TOG figures on some listings give a clearer insulation claim than marketing words alone.
What is the warmest thermal underwear?
Listings that state a higher TOG or fleece lining are aiming for more insulation. In this guide Undercover quotes 0.75 TOG and CL convallaria describes fleece-lined midweight fabric; compare those details rather than a lab test from us.
