Best thermal base layers 2026

Top-rated thermals do more than just keep you warm.

If you’re serious about getting outside in all conditions, don’t underestimate the importance of a good base layer. No matter how thick your fleece, jacket and trousers are, poor thermals will make you less comfortable.

The best ones adapt to changes in your body heat, so if you’re taking a break from your hike to check out the views, your body temperature won’t plummet. But keeping you insulated is only half the story: our customer survey reveals the thermals that wick away sweat quickly to keep you dry, that are made of fabrics which feel soft against your skin, and that are durable.

Three brands met our standards to be named Which? Recommended Brands, where members spent an average of £40-£72 per thermal. But there's also a highly rated bargain brand, coming in at £18 on average, that's fantastic for everyday wear. Read on for the top recommendations from genuine customers that will match your budget.

What are the best thermal base layer brands according to Which? members?

We've asked customers to review a lot of their outdoor gear including walking boots and waterproof jackets, plus where we recommend to buy them in our guide to the best outdoor retailers.

Which? Recommended thermal base layer brands

Icebreaker, Which? Recommended Brand

Verdict: Ultra-durable, exceptionally warm and worth every penny

Customer score: 92%

Average price paid: £72

Pros:

• Earned an impressive customer score
• Made from premium materials
• Truly long-lasting

Cons:

• Pricier than most

Described by one customer as ‘the Rolls-Royce of base layers’, Icebreaker claimed the top spot in our table. Most of its thermals are made from merino wool but come in different weights, from a light 150g when mild to a heavy 260g for freezing conditions. Like many brands, it also has thermals made of a blend of wool together with other materials, such as elastane, for extra durability or stretch. 

Icebreaker’s thermals earned five stars for comfort and they adapt superbly to changing temperatures. They also have top-tier odour resistance, so users said they didn’t need to wash their thermal each time they wore them.

With respondents paying £72 on average, there’s no avoiding the high price, but this brand should last. One customer of 30 years said: ‘The oldest ones are still serviceable for cold days in the garden.’ Another said: ‘Shirts last many years without developing holes or snags, even worn under backpacks.’

Shop Icebreaker thermals direct, or retailers such as Ellis Brigham, Alpine Trek or Cotswold Outdoor. It also has some discounted stock in its outlet online here.

Rohan, Which? Recommended Brand

Verdict: Reliable at keeping you warm, drying quickly and lasting the test of time

Customer score: 90%

Average price paid: £42

Pros:

• Fit well
• Lightweight while keeping you warm
• Resilient through the washing machine

Cons:

• Expensive at full price

Rohan's thermal base layers were praised by many for being warm without feeling bulky under other clothes. One said: 'The fabric is quite sheer, yet durable, so is very comfortable, lightweight and unobtrusive – like a second skin.' Plus, they adapt well to changing temperatures. One customer told us they 'initially bought for winter wear, but in the north-west of England it's suitable for daily wear for most of the year'.

Its thermals are made from a variety of materials, including synthetic blends designed to dry fast, wick away sweat quickly, and survive lots of washes. The merino wool blends aim to balance the warmth and odour resistance you get from wool with the stretch and durability of synthetics. 

Owners also said they last really well, keep their shape, and dry 'astonishingly speedily'. This makes them highly practical for daily use and travelling and one customer has had some Rohan thermals for more than a decade. The fit was pleasing too, with customers mentioning generous sleeve and body lengths, as well as useful thumb holes.  

Rohan thermals aren't cheap, but our respondents felt they were generally great value for money. One wearer told us: 'Not the cheapest brand but by far the best value for money in relation to their quality, their finish, their durability and their washability.'

You can buy Rohan thermal base layers direct from its website, or from one of its physical shops.

Helly Hansen, Which? Recommended Brand

Verdict: Soft and comfortable against your skin, while keeping the chill at bay

Customer score: 85%

Average price paid: £40

Pros:

• Well insulated
• Easy to clean
• Very breathable

Cons:

• Prices are likely a bit steep for some

Long-time thermal wearers told us they can depend on Helly Hansen's thermal base layers. One outdoor enthusiast told us: 'As a lifelong skier, I have tried many different thermal base layers over the years. For comfort, style and above all, thermal protection, I would say the Helly Hansen gear is the best I have tried.' Others said that its thermals brilliantly block out sharp winds and the cold of early morning runs.

While some high-street brands rely solely on standard polyester as a synthetic, water-wicking fibre, some Helly Hansen thermals use polypropylene, which is more hydrophobic – that means it can't absorb moisture and pushes sweat away from the skin.

The warmest Helly Hansen thermals incorporate a layer of merino wool into the blend. Customers said they found these materials soft and comfortable, with one reviewer stating there was 'no itching [and they] can be hung up to self-clean after use, as you can with good wool products. [It] doesn't retain smell and wears well.' They survive repeated washing well too, with one wearer noting that the material 'stays wonderfully white'. 

A handful of people said that some fits didn't suit them, so check their shape and length before you commit. Helly Hansen's often high prices might sting, but buyers advise waiting for the sales when you can pick up items at a discount.

Browse Helly Hansen's thermals online or visit one of its stores.

Our cheaper pick for thermal base layers

Uniqlo

Verdict: Stylish, budget-friendly and thin enough to layer under almost anything

Customer score: 88%

Average price paid: £18

Pros:

• Attractive prices
• Choice of materials for different temperatures
• Soft against your skin

Cons:

• No brand warranty

Uniqlo’s HeatTech thermals trap your body heat in thin, stretchy fabrics that fit easily under everyday clothes. It has standard, extra warm and ultra warm ranges, some of which incorporate cashmere into the blend. Its thermals give wearers warmth without feeling like a thick, stiff layer. One respondent said: ‘I don’t really notice them – they are very comfortable and flexible. Other base layers I’ve had in the past hinder mobility.’ Another liked how they were ‘figure-hugging without being tight’ while being ‘soft and gentle on the skin’.

From short-sleeved crewnecks to long-sleeved turtlenecks, the choice of styles is also popular, and with a variety of patterns and colours, they look less like basic thermals. Uniqlo thermals don’t come with a warranty as, say Icebreaker garments do, but with respondents telling us they cost £18 on average, we think they're a steal.