The baselayers I'm taking to -25: merino, synthetic, and why I split the two

This started with a shirt I already own, and a problem I have never quite solved. I have a week booked in Kittila, in northern Finland, above the Arctic Circle, this winter. It is the same active week behind the down jacket piece and the winter boots piece that sit alongside this one: a 35km snowmobile tour, a 10km husky-sledding run, the local snow village, fell hikes if the weather allows, and northern-lights watching at night when the temperature drops to around minus twenty-five. Polar night, so no midday sun to lean on, and long static hours in the cold.

The baselayer is the one piece of that kit I thought I had sorted, because I wear merino every single day of a British winter. I live in a light Icebreaker for hiking, for dog walks on the Purbeck coast, for standing on a touchline coaching under-nines football in the sleet. I rate it as highly as any bit of clothing I own. So you would think a warmer merino top for Finland was a simple upgrade.

It is not, and the reason is a bit embarrassing. I cannot wear merino on my top half without itching. I am fine with it on my legs, I love it against my arms in a light top, but a proper thick merino layer on my chest and back drives me up the wall within the hour. So the plan for minus twenty-five is not "buy more merino". It is to split the system: merino where it does not itch, synthetic where it does. That is the whole piece, and I have not seen anyone else say it out loud. This sits under our wider cold-weather gear hub, where the rest of the kit for an active Arctic week lives.

The thing I have to admit: merino makes my top half itch

Let me be straight about my own kit before I recommend anyone else's. I own the Icebreaker Merino 175 Everyday, the lightest of their 100% merino tops, and I have worn it to death. It is 175gsm of fine merino, next-to-skin soft, and for three seasons of British hill walking it is the first thing I reach for. I do not itch in it. I have never itched in it.

Push up a weight or two, though, to a thick 250 or 260gsm merino top, and my chest and back start to prickle and I want it off. I have tested this on myself more than once, because I kept assuming I would grow out of it or that a nicer wool would fix it. It has not, and it does not. Whatever the fibre count on the label, thick merino on my torso itches, and a light one does not.

My working theory, and it is only a theory, is that it comes down to how the fabric sits. My legs are hairy enough that a merino legging never actually lands flat against the skin, so the tiny prickle of the fibre ends never really connects. On my chest and back the fabric sits tight and flat against bare skin, and every fibre end gets to do its work. A thin 175gsm top has less of that to give, so it slips under my threshold. A dense 260 does not. I could be completely wrong about the mechanism. What I am not wrong about is the outcome: I can wear merino on my legs all day and I cannot wear a thick merino top for an hour. If that is you too, you are not imagining it and you are not being fussy.

The idea nobody says out loud: split the system

Every baselayer article I have ever read treats this as a whole-body choice. Merino person or synthetic person. Team wool or team plastic. You pick a side and you buy head-to-toe in it.

That framing is wrong, or at least it is wrong for people like me, and I suspect there are a lot of us. There is no rule that says the fabric on your legs has to match the fabric on your chest. Your legs and your torso are different jobs, worn against different skin, doing different amounts of work. So treat them as two decisions, not one.

For me the split is obvious once you say it. Merino on the legs, where it never itches and where its warmth-for-weight and odour resistance are a real gift over a week of activity. Synthetic on top, where wool will not sit comfortably against my skin and where, as it turns out, I give up almost nothing by going wool-free anyway. One body, two fabrics, each chosen for where it actually touches me.

If you get on with merino everywhere, wonderful, wear it head to toe and ignore me. But if the only thing stopping you buying a baselayer is that a wool top makes you miserable, do not write off the whole idea of a baselayer. Split it. That is the point of this piece, and it is the bit the roundups miss.

If merino itches, a synthetic top still beats no baselayer

This is the part I most want to get across, because I think the merino-versus-synthetic argument scares people out of wearing anything at all. If you have decided you cannot stand merino, and you have been told merino is the only "proper" baselayer, the quiet conclusion a lot of people reach is to skip the baselayer and just pull a fleece straight over a cotton tee. That is the worst thing you can do, and it is worth understanding why.

A baselayer keeps you warm in two ways, and only two. First, it traps a thin layer of still air against your skin, and still air is what actually insulates you. Second, it wicks sweat off your skin and moves it outward, so that when you stop climbing and your body cools, you are not sitting in a wet film that pulls the heat straight out of you. Warmth and dryness. That is the entire job.

A synthetic top does both. It traps still air, and on the wicking side it is as good as merino or better, because moving moisture is exactly what polyester and polypropylene were engineered to do. What you give up going wool-free is small: a little warmth-for-weight, and a top that starts to smell faster after a couple of hard days, which is why the better synthetics such as the Montane Dart build in a Polygiene anti-odour treatment. On warmth the two fabrics are closer than the internet pretends, and on wicking synthetic is right there.

The only top that is actually worse than wearing nothing is cotton. A cotton tee soaks up your sweat, holds it against your skin, stops wicking, and then chills you hard the moment you stop moving. In real cold that is not just uncomfortable, it is how people get into trouble. Cotton kills. So if merino and your skin have fallen out, the answer is not "no baselayer". The answer is a wool-free synthetic top, which is far better than nothing and very nearly as good as the wool you cannot wear.

Static versus active: warmth comes from the system

The other thing worth saying, before anyone spends money chasing the "warmest" baselayer, is that no single layer keeps you warm at minus twenty-five. The warmth comes from the system: baselayer, then a midlayer, then a shell, each doing a slice of the work. Trying to solve deep cold by buying one heroic thick top is a way to be sweaty on the climb and cold at the top.

It matters even more on a trip like mine because the day swings between two states. On the way up a fell I am working hard, generating heat, and the baselayer's main job is to move sweat off me fast. Standing under the aurora on a frozen lake an hour later, making almost no heat of my own, the same baselayer's job flips to trapping every scrap of warmth I have left. A good layering system handles both. One panic-bought heavyweight top handles neither well.

So my thinking for the coldest, most static moments is not one magic garment. It is a stack: a warm brushed synthetic top against the skin, the Under Armour ColdGear I already own as a mid-weight layer over it, then the insulation and shell on top. On the legs, merino leggings under trousers. The baselayer is the foundation of that stack, not the whole building, and it is worth choosing on that basis rather than on a single warmth number.

If you want the full head-to-toe breakdown of weights and how to build a layering system, that lives in the complete baselayers guide. This piece is narrower: it is about the fabric split, and the specific tops and leggings I would actually buy for it.

The merino tops I rate (and live in)

If you get on with merino, this is where I would start, because a good merino top is a lovely thing to wear and I am not talking anyone out of it. I am only talking myself out of it, and only above a certain weight. The rough weight bands to hold in your head: light is around 150 to 175gsm, mid is 200 to 250gsm, and heavy is up around 320gsm. The heavier you go, the warmer and the more prone to itch on sensitive skin.

Icebreaker Merino 175 Everyday. The one I actually own and live in. 175gsm of 100% merino, light, soft, and the top I wear for most of a British winter. It is not a minus-twenty-five top on its own, it is a light everyday baselayer, but as the against-skin layer in a system it is superb, and it is the one weight of merino my own skin is happy with. If you are new to merino, start here.

Icebreaker 200 Oasis. Icebreaker's best-selling baselayer, and the mid-weight step up at 200gsm. A touch warmer than the 175, still soft and everyday, and the sensible all-round choice for cold-weather layering if merino suits you. This is roughly the weight at which my own top half starts to notice the wool, so your mileage will depend on your skin.

Icebreaker 260 Tech. The heavyweight of Icebreaker's 100% merino line at 260gsm, and the one a lot of people reach for when the forecast turns properly cold. For a merino wearer heading somewhere like Finland, this is the warm merino top to have. Two honest notes: at 260gsm it is exactly the weight my torso cannot tolerate, and when I looked it was thin on stock across several sizes, so if it fits your skin better than mine, grab your size when you see it.

Smartwool Classic Thermal Merino. Smartwool's 250gsm interlock-knit crew, a mid-to-heavy 100% merino top in the same tier as the 260 Tech and a strong alternative if you prefer Smartwool's fit. Warm, well made, and a proper cold-weather merino layer for people whose skin is happier in wool than mine.

Helly Hansen Lifa Merino Midweight Crew. This one is clever and worth a look if you are on the fence like me. It is a 225gsm two-layer build: merino on the outside for warmth, but Helly Hansen's Lifa polypropylene knitted on the inside, so it is synthetic, not wool, that actually sits against your skin. In theory that is exactly the fix for an itch problem, wool warmth with a plastic face. I am getting one to test through this winter, because if the plastic face really does keep the wool off my skin, it could be the best top I own for a trip like this: merino warmth and merino odour resistance over a week, without the prickle that stops me wearing wool on my chest.

Budget merino: Merino.tech and Danish Endurance sets. If you want to try merino without the Icebreaker price, both do well-reviewed value sets. The Merino.tech line comes in three weights (a 165 lite, a 250 mid and a 320 heavy) and the sets include a pair of merino socks, which is good value for a first go. Danish Endurance's sets are a merino-polyamide blend rather than pure wool, which makes them a little tougher and a little cheaper. Neither is quite the fabric of a premium Icebreaker, but both are a sensible way to find out whether merino and your skin agree before you spend more.

The wool-free tops, if merino and you do not get on

This is my half of the split, and the section I would point any fellow itcher at. None of these is wool, all of them do the two jobs of a baselayer, and the warm end of the range is close enough to merino that you are not giving up your week to spare your skin.

Odlo Performance Warm. This is the top I am taking for the cold, static hours, and my pick of the wool-free tops for genuine cold. It is a warm, brushed-back recycled synthetic that Odlo rate for a comfort range down into serious cold, with their ZeroScent treatment to keep the smell down. Worn against the skin under my ColdGear, this is the wool-free answer to a heavyweight merino top, and it is the one that gives me the warmth I would otherwise have had to itch for.

Under Armour ColdGear Fitted Mock. I own this one and have worn it for winter gym sessions and cold morning runs for a couple of years. It is a dual-layer fabric: a warm brushed inside face and a smooth fast-drying outer, in Under Armour's ColdGear line, which is their warm range. Do not confuse it with their HeatGear, which is the opposite, a thin hot-weather compression fabric. For Finland the ColdGear becomes my mid-weight synthetic layer over the Odlo, a job it is well suited to, and it is a proven bit of my own kit rather than something off a spec sheet.

Montane Dart Long Sleeve. The everyday wool-free top I would recommend to most people. It is a light recycled-polyester baselayer with Montane's Polygiene permanent anti-odour treatment built in, which is the sensible answer to synthetic's one real weakness, that it starts to smell faster than wool. It is a wicking-first active layer rather than a heavyweight warmth piece, so it shines on the move and as the against-skin layer in a stack. Montane also make a warmer brushed version, the Dart XT, if you want the same top with more heat in it.

HH Lifa Stripe Crew. The cheap wool-free hero. It is 100% Lifa polypropylene at around 125gsm, so it is light and thin, and it is one of the best pure wicking layers you can buy: polypropylene barely holds 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, but at its price it is the answer to the "I cannot wear wool so I will skip the baselayer" mistake. Buy one, wear it under everything, stop wearing cotton.

OEX Barneo. 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, wick well and resist odour, and this one adds thumb loops and low-bulk seams. It is a lightweight, all-year top rather than a deep-cold one, but it is an easy, affordable UK buy and a comfortable wool-free option for milder cold and as a base in a system.

Merino where it never itches: the legs

Here is the other half of the split, and the easy half. On my legs I want merino, and I want it at the warm end. Merino's warmth-for-weight, its warmth even when slightly damp, and its resistance to smell over a week of activity are all real advantages, and none of the itch that stops me on my chest ever shows up on my legs. If the theory about hairy legs holding the fabric off the skin is right, that is why. Either way, this is the part of me that is straightforwardly a merino wearer.

Icebreaker 260 Tech Leggings. My pick for the legs. A 260gsm 100% merino legging, slim-fit so it layers cleanly under trousers, with a gusset for movement and flatlock seams so nothing rubs on a long day. It is the bottom-half partner to the 260 Tech top, and the weight I want against my legs for standing around at minus twenty-five. This is the merino I can wear.

Budget legs: the Merino.tech 320. If you do not want to pay Icebreaker money for something that lives under your trousers all week, Merino.tech's 320gsm bottoms are the heaviest weight in their line and a warm, sensible value pick for the legs. On kit that never shows and only has to be warm, spending less here to spend more on your jacket and boots is a fair trade.

What I am actually packing for -25

Pulling the split together, here is the plan for the coldest, most static parts of the week, the aurora vigils and the sled seats where I make almost no heat of my own:

• On top: this is the one I am still deciding, and I am testing two setups through the UK winter before I commit either to Finland. The first is the Helly Hansen Lifa Merino Midweight, which puts polypropylene against my skin and merino on the outside, so if it beats the itch I get wool's warmth and week-long odour resistance without the prickle. The second is the Odlo Performance Warm, a pure synthetic that sidesteps wool entirely. Whichever my skin gets on with over a few cold months is the one I pack, worn under the Under Armour ColdGear I already own. I would far rather learn which works on a wet Purbeck hill in December than on a frozen lake in Lapland.
• On the legs: merino, and warm merino at that, the Icebreaker 260 Tech Leggings under my trousers. This is the half of me that is happily a merino wearer, so it gets the wool.
• For the active days: the light Icebreaker 175 I live in on the milder, moving fell days when the job is wicking more than warmth, and I am working hard enough not to notice the wool. On the hardest static days it is synthetic on top, merino on the legs, all the way.

None of that is a single hero garment. It is a system, split down the middle by fabric, chosen for where each fabric actually touches me. The insulation and shell that go over the top of it get their own treatment in the down jacket piece. I will report back on which top won the winter test, how the split actually held up at minus twenty-five, and whether my hairy-legs theory survives contact with an Arctic aurora night. That write-up is coming once I am home.

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