Best base layers for hiking UK 2026: merino and wool-free, every weight band

Most people obsess over the jacket and the boots and give almost no thought to the layer underneath everything. That is the wrong order. The base layer is the one piece of kit that sits directly against your skin from the first step to the last, and its job is simple: keep you warm by trapping a thin layer of still air, and keep you dry by moving sweat off your skin so you are not sitting in a cold, wet film when you stop. Warmth and dryness. Get that layer right and the rest of your clothing works better. Get it wrong and no jacket saves you.

Unlike boots or waterproofs, a base layer is not a seasonal buy. It is an all-year piece: a light one for warm days and hard-working walks, a heavier one for standing still in the cold, and often two or three in the drawer for different conditions. So this guide is built around weight, not season. Light, mid and heavy, in both merino and wool-free, with an honest note on who each one is for.

For what it is worth, I live in a light Icebreaker 175 for most of a British winter, and I own an Under Armour ColdGear that has done a couple of years of cold gym sessions. Those two I can talk about from the skin out. The rest are chosen on fabric, weight, reviews and how each fits into a layering system. This is the hub for our whole base layer cluster, so where a brand has its own full guide I have linked down to it.

Every base layer in this guide, compared

The whole guide in one table. Tap a name to jump to the write-up, or the buy button to check today's price. Prices move with size and colour, so treat these as a guide.

Merino vs synthetic, honestly

This is the argument that dominates every base layer conversation, and it is more even than the internet pretends.

Merino wool is the fibre most people rate, and for good reason. It has a slight edge on warmth-for-weight, it stays warmer than synthetic when it is slightly damp, and it resists odour better than anything else, which really matters over a multi-day trip when you are wearing the same top for days. It also feels soft and natural against the skin. The trade-offs are real, though: it costs more, it is less durable than synthetic on its own, which is why the best value merino is usually blended with a little nylon or polyamide, and on some people a thick wool top itches.

Synthetic (polyester and polypropylene) does the two core jobs at least as well. On wicking it is right there with merino or better, because moving moisture is exactly what these fibres were engineered to do, and it dries faster. It is cheaper and tougher. Its one honest weakness is smell: synthetic starts to pong faster than wool after a hard day, which is why the better ones such as the Montane Dart build in a permanent Polygiene anti-odour treatment.

Here is the part most guides skip. If merino itches you, a good synthetic top is very nearly as good and far better than going without. The one material that is actually worse than nothing is cotton: it soaks up sweat, holds it against your skin, stops wicking, and chills you hard the moment you stop. In real cold that is not just uncomfortable, it is how people get into trouble. So the honest ranking is merino and synthetic both good, cotton bad. If wool tops and your skin do not get on, we have a full guide to the best non-merino and synthetic base layers that goes into it properly.

Weight bands: light, mid and heavy

Base layers are sold by fabric weight in grams per square metre (gsm), and that number tells you far more about what a layer is for than the season on the label. Three rough bands are worth holding in your head:

Light, around 125 to 175gsm. Thin, breathable, wicking-first. This is the band you want for working hard on the move, for warmer days, and as the against-skin layer in a cold-weather stack where a heavier layer goes over the top. The Icebreaker 175 I live in sits here, as do the wool-free HH Lifa Stripe and Montane Dart. A light layer is the most useful all-rounder for most UK hiking.

Mid, around 200 to 250gsm. The three-season workhorse. Warm enough to wear on its own on a cold day, thin enough to layer, and the sensible single buy if you are only buying one. The Icebreaker 200 Oasis and the two-layer HH Lifa Merino Midweight live here.

Heavy, around 250 to 320gsm. Warmth first. These come into their own when you are not making much heat of your own: standing still, slow walking, sitting in the cold, or seriously low temperatures. They are too warm for hard uphill work, when you will sweat through them. The Smartwool Classic Thermal 250 and Icebreaker 260 Tech are the heavy merino picks, and Merino.tech's 320 is the budget option.

The mistake to avoid is buying one heavy top and expecting it to do everything. In deep cold the warmth comes from the whole system, base plus mid plus shell, not from one heroic layer. A heavy base on a hard climb just leaves you soaked.

Fit: compression vs relaxed

Base layers come in two broad fits, and it is worth knowing which you are buying.

Compression layers are tight and elastic, sold on muscle support and a fast-drying, second-skin feel. Under Armour's HeatGear is the obvious example, though that is a hot-weather compression fabric built to keep you cool and should never be treated as a cold-weather pick. There are compression options with warmth too, such as Under Armour's ColdGear Compression and the Canterbury Thermoreg range. Some people love the locked-in feel, particularly for high-output stuff like running.

Relaxed or standard fits sit close to the body without squeezing. For long days of walking, and especially for warmth, most people are more comfortable in a relaxed fit: it traps that layer of still air a little better, and it does not feel like it is gripping you five hours in. The Icebreaker 175 and most merino tops are cut this way, close but not compressive.

There is no right answer, only a preference. If you already know you like compression from the gym, a fitted synthetic will suit you. If you are buying a layer to keep you warm and comfortable over a full day out, a relaxed merino or synthetic is the safer default.

Split the system: different fabric top and bottom

Here is the idea most roundups miss, and the one that changed how I buy base layers. There is no rule that the fabric on your legs has to match the fabric on your top. Your torso and your legs sit against different skin and do different amounts of work, so treat them as two separate decisions.

For me this is not theory. I wear merino happily on my legs all winter, where it never itches, but I cannot wear a thick merino top: above a certain weight it prickles my chest and back within the hour. My working theory is that my legs are hairy enough to hold the fabric slightly off the skin, so the fibre ends never quite land, whereas on my torso the fabric sits flat against bare skin and every fibre gets to work. I could be wrong about the mechanism. I am not wrong that a light 175 top is fine and a heavy 260 is not, while merino leggings never bother me at all.

So my own kit splits down the middle: merino on the legs, where its warmth and odour resistance are a real gift, and a wool-free synthetic on top, where I give up almost nothing and spare my skin. If you get on with wool everywhere, wear it head to toe and ignore me. But if the only thing putting you off a base layer is that wool tops make you miserable, do not skip the base layer. Split it. I wrote about this at length in the base layers I am taking to minus twenty-five in Finland, and the wool-free half of the split has its own full guide to non-merino base layers.

Looking after a base layer

Base layers last longer and keep working better with a bit of care, and merino in particular rewards it.

Wash cool, around 30 degrees, and turn the garment inside out first. Use a small amount of detergent, and for merino a dedicated wool wash is worth it. Never use fabric softener: it coats the fibres and kills both merino's natural properties and synthetic's wicking. Do not tumble dry, which is the fastest way to shrink wool and cook the elastane out of a synthetic. Dry flat or on a line.

One of merino's quiet advantages is that it needs washing far less often than synthetic, because it resists odour so well. Air it out overnight and it is usually good for another day, which is exactly why it earns its place on a multi-day trip. Synthetic you will wash more often. Either way, cool wash, no softener, no tumble dryer, and both will give you years.

The best base layers UK 2026

Sorted by weight band, then by fabric. Every pick lists which band it sits in and who it is for. Where I own the item I have said so; everything else is a buyer's assessment based on fabric, weight and reviews.

Light band (around 125 to 175gsm)

Icebreaker 175 Everyday Crew: the light merino I live in

Light band, merino. This is the one I actually own and wear to death: 175gsm of 100% merino, next-to-skin soft, and the first thing I reach for through most of a British winter, hiking, walking the dog on the Purbeck coast, standing on a touchline coaching kids' football in the sleet. It is not a heavyweight and it is not trying to be. It is a light everyday base layer, superb on the move and as the against-skin layer in a colder stack, and crucially it is the one weight of merino my own skin is completely happy with. If you are new to merino, start here. Icebreaker is the benchmark brand for a reason, and our full guide to Icebreaker base layers breaks down the whole range.

HH Lifa Stripe Crew: the cheap wool-free hero

Light band, wool-free. The best value layer in this whole guide, and my pick for anyone who cannot wear wool. It is 100% Lifa polypropylene at around 125gsm, so it is light and thin, and it is one of the best pure wicking layers money can buy: polypropylene barely holds any water at all, so it moves sweat off your skin fast and dries almost instantly. It is not a warm top on its own, it is a moisture-management layer to wear under everything else. At around the price of a decent pizza it is the direct answer to the "I cannot wear merino so I will just skip the base layer" mistake. Buy one, wear it under your mid-layer, stop wearing cotton. There is more on Helly Hansen's Lifa range in our full guide to Helly Hansen base layers.

Montane Dart Long Sleeve: the wool-free everyday active top

Light band, wool-free. The synthetic top I would recommend to most people who want a proper active base layer without wool. It is a light 100% recycled-polyester layer with Montane's Polygiene permanent anti-odour treatment built in, which is the sensible fix for synthetic's one real weakness, that it starts to smell faster than wool. It is wicking-first rather than a warmth piece, so it shines when you are working hard and as the base in a stack. Montane also make a warmer brushed version, the Dart XT, if you want the same idea with more heat in it. A well-reviewed, well-made British-brand pick.

OEX Barneo Top: the soft bamboo-blend option

Light band, wool-free (plant blend). A bamboo-blend top from Blacks' own OEX label, mixing bamboo-derived fibre with polyamide and a little elastane. Bamboo blends feel soft and cool against the skin, closer to cotton in feel than a slick synthetic, while still wicking well and resisting odour. This one adds thumb loops and low-bulk seams. It is a light, all-year layer rather than a deep-cold one, but it is an easy, affordable UK buy and a comfortable wool-free option for milder cold and everyday wear. It is a Millets exclusive. Our OEX Barneo bamboo review has the full assessment.

Mammut Ducan FL Longsleeve: the premium wool-free active top

Wool-free, light. If you want a synthetic active top a clear step up from the budget wickers, this is it. The Ducan FL is a 100% recycled polyester top at around 150g, with a stretchy athletic fit and a bio-based HeiQ Fresh treatment to keep the smell down on long days. It wicks and dries fast, it is genuinely light, and being wool-free it suits anyone who cannot wear merino. At around £55 it is premium for a synthetic top, but it is Mammut build quality and it earns its place if you run hot and move hard. Full detail in the Mammut Ducan FL review.

Mid band (around 200 to 250gsm)

Icebreaker 200 Oasis: the best all-round pick

Mid band, merino. Icebreaker's best-selling base layer, and the one I would point most people at first. At 200gsm of 100% merino it is a step up in warmth from the 175, still soft and everyday, with underarm gussets and offset shoulder seams so a pack strap does not chafe. It is the sensible single buy if you are only buying one merino top: warm enough for a cold day on its own, thin enough to layer under a jacket. This is roughly the weight at which my own top half starts to notice the wool, so how you get on will come down to your skin, but for most people the 200 Oasis is the safe, do-everything choice. See the full Icebreaker guide for how it sits against the rest of the range.

HH Lifa Merino Midweight: the clever hybrid

Mid band, merino outer with synthetic face. This one is worth a proper look if you are on the fence about wool like me. It is a 225gsm two-layer build: 100% merino on the outside for warmth, but Helly Hansen's Lifa synthetic knitted on the inside, so it is plastic, not wool, that actually sits against your skin. Helly Hansen sell it as non-itch, and in theory that is exactly the fix for an itch problem, wool warmth with a synthetic face and better moisture-pulling from the Lifa layer. Of all the merino-branded tops, it is the one I would try first on sensitive skin. More on it in the Helly Hansen base layers guide.

Merino.tech Merino Set: the best budget way into merino

Mid band (and beyond), merino. If you want to try real merino without the Icebreaker price, this is where I would start. Merino.tech do a well-reviewed 100% merino set that comes in three weights, a 165 light, a 250 mid and a 320 heavy, and the set includes a top, leggings and a pair of merino socks, which is good value for a first go. The review count on this range runs into the thousands, though that is at brand and variant level rather than for a single garment, so read it as "a lot of people buy this" rather than a score for one exact top. It is not quite the fabric of a premium Icebreaker, but it is a sensible, low-cost way to find out whether merino and your skin agree before you spend more, top and bottom in one go.

Danish Endurance Merino Set: the best value matched set

Mid band, merino blend. Danish Endurance have built a strong reputation on well-made value kit, and their base layer set is a sensible middle ground between budget and premium. The core range is an 80% merino, 20% polyamide blend rather than pure wool, which makes it a little tougher and a little cheaper than 100% merino, with a warmer 90/10 option in the range too. You get a matched top and leggings that will take more of a kicking than pure wool. If you have used their excellent merino hiking socks you already know the brand does honest kit at a fair price. The full Danish Endurance base layers guide has the detail.

Mammut Trift: the premium merino set

Merino, premium. The Trift is Mammut's merino baselayer, a merino and polyamide blend in a seamless, body-mapped knit that pairs wool's warmth and low odour with synthetic durability and quick drying. It comes as a longsleeve top and matching long tights, so you can run merino head to toe. It is a premium price, around £100 for the top and similar for the tights, but for cold, stop-start days where merino shines it is a lovely set, provided wool suits your skin. Full detail in the Mammut Trift review.

Heavy band (around 250 to 320gsm)

Smartwool Classic Thermal 250: the heavy merino for cold

Heavy band, merino. Smartwool have been making merino base layers for decades, and the Classic Thermal is their warmest, a 250gsm 100% merino interlock knit with flatlock seams and offset shoulders to keep it comfortable under a pack. This is a proper cold-weather top: warm, soft and made for the days when warmth matters more than breathability, or when you are not working hard enough to overheat. For a merino wearer, it is the heavy top I would put ahead of most, and a strong alternative to the Icebreaker 260 if you prefer Smartwool's fit. Smartwool also cut their lighter All-Season blend in a women's fit, and the women's All-Season long sleeve is one of their best sellers. Our Smartwool base layers guide covers the rest of the range.

Icebreaker 260 Tech: the warmest 100% merino

Heavy band, merino. The heavyweight of Icebreaker's 100% merino line at 260gsm, and the top a lot of committed merino wearers reach for when the forecast turns properly cold. If wool suits you and you are heading somewhere seriously cold, this is the warm merino top to have, and it is my own pick on the legs in leggings form for standing around in deep cold. Two honest notes: at 260gsm this is exactly the weight my torso cannot tolerate, so it is a top for people whose skin is happier in wool than mine, and at the time of writing the crew is out of stock across sizes while the leggings are still available on low stock. Worth grabbing your size when it comes back if it is your fabric.

Under Armour ColdGear: the warm wool-free layer I own

Heavy-ish band, wool-free. I own this one and have worn it for winter gym sessions and cold mornings for a couple of years, so I can speak to it directly. It is a dual-layer fabric: a warm brushed inside face against the skin and a smooth, fast-drying outer, in Under Armour's ColdGear line, which is their warm range. The important thing, and the thing people get wrong, is not to confuse ColdGear with HeatGear: HeatGear is the opposite, a thin hot-weather compression fabric built to keep you cool, and it should never be treated as a cold-weather layer. In a cold-weather system I use the ColdGear as a warm mid-layer over a lighter wool-free base. If you are weighing the two lines up, our ColdGear vs HeatGear guide spells out exactly which is which.

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