Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top review: a super-warm and cozy base layer for high-intensity activity

Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top: first impressions

Merino wool has long been the standard bearer when it comes to high-performing fabrics for warm and versatile base layers. Sure, many brands have tried to sell polyester as the best, and bamboo has even had its day in the sun. But, in my humble opinion, nothing beats natural Merino wool.

It’s warm, cozy and doesn’t absorb odors, meaning it’s more pleasant on those longer multi-dayers or other trips where your kit won’t see a wash for a while. And it’s good for the environment, too. You see, whereas polyester is a manmade synthetic fabric, Merino wool is grown by Merino sheep year-round. Much like regular wool, these sheep actually grow too much of it, meaning we can siphon off a little for ourselves and turn it into some of the best kit out there – all while causing zero harm to the animals and promoting sustainable farming practices.

Icebreaker is a New Zealand brand that has been leading the charge on the switch to Merino since 1995 and has become one of the standout players in the space. That’s why, when I was given the opportunity to test their Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top earlier this year, I jumped at the chance, charging head first into a base layer bonanza with expectations as high as this top’s price tag.

In a nutshell, the Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top is the brand’s warmest active layer designed for high-output pursuits like winter hikes, skiing and mountaineering. It’s manufactured from 100% Merino wool and comes with a handful of extra features that make this top a joy to wear. But let’s look at the elephant in the room: costing $175 (US) / £125 (UK) when bought directly from the brand, this base layer is a costly investment, especially when you compare it with simple polyester base layers you can picked up in most places for less than £30. So why the high price tag? And is it worth it?

Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top: in the wild

I first got my hands on a sample of the Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top way back at the start of September. The weather was way too balmy to give it a real test back then, so I had to wait a little until I could properly take it for a spin. Thankfully, a late October trip to Utah, USA, had me out on all sorts of early morning hikes in near-freezing temperatures where I got to put this Merino base layer through its paces.

After my return to the UK, I also wore it on a handful of chilly trail runs and country walks, a two-day backpacking trip in Bannau Brycheiniog (the Brecon Beacons) and, thanks to it being oh-so-comfy, to a mid-November Christmas market where a cold snap brought us some festive snow and a temperature of 30°F (-1°C). Therefore, despite not wearing this thing up Annapurna I or running a lumpy ultra in it, I was still able to put it through the full gamut of conditions it will likely ever come across, and I’m confident in my assessment of the 260 ZoneKnit Thermal Top. So let’s jump in.

Firstly, this thing is thick; much more so than the base layers I’ve become used to over the years. In fact, since around 2021, Icebreaker’s thinner Merino 175 Everyday Long Sleeve Half Zip Thermal Top has been my go-to base layer on winter runs and year-round camping trips, and this version feels at least twice as thick as that. But only in the parts that you need the warmth.

You see, unlike the basic (yet still excellent) design of the 175 Everyday base layer, this new version is designed with Icebreaker’s ZoneKnit engineering, meaning that the weave is concentrated on the areas you want to keep warm most. When active in cold temperatures, that means your chest, your shoulders and your arms, which is exactly what the design of this base layer prioritizes. The rest of the garment, namely the back, your hips and from your armpits down is cut from a thinner Merino weave, optimizing breathability in these places and ensuring you don’t build up too much of a sweat.

Based on that cut, Icebreaker has nailed it when it comes to delivering comfortable warmth. In fact, as I write this, I’m sitting at my desk in my chilly office wearing this base layer under a thin jumper and I’m more than comfortable. More than I should be in so few layers, at least. During testing, I was comfortably warm when I wore it under a thin fleece and a Mountain Equipment Lightline standing around a Christmas market in temperatures of around 30°F (-1°C) for three hours, and I was comfortably warm wearing it under a Patagonia Nano Puff hoodie hiking through the Utah backcountry in temperatures approaching freezing.

In fact, even when I wore this thing on trail runs in temperatures hovering around 41°F-45°F (5°C-7°C), I still remained comfortable (despite expecting I’d be too warm), especially when combined with the equally excellent Icebreaker Merino Blend 200 Realfleece Descender Long Sleeve Zip Hoodie. That’s down to the incredible way this base layer breathes, repelling sweat and allowing moisture to travel away from the skin better than any other base layer I’ve ever tried.

Naturally, being a type of wool, it will still absorb some of that moisture and remain wetter for longer than the likes of quick-drying polyester. But my body heat always dried this base layer out on its own, without the need for me to ever hang it up, wring it out or do anything whatsoever other than wait. In that sense, I find this base layer does a phenomenal job of keeping you comfortable over a huge temperature range, working well in sub-zero temperatures all the way to around 45°F-46°F (7°C-8°C).

As is commonplace with Merino garments, the 260 ZoneKnit Long Sleeve Half Zip Thermal Top also continues to keep you warm long after it’s become wet. Granted, wearing a wet woollen top isn’t a comfortable experience, but on the times I sweat enough into this that wet patches appeared, I never felt cold spots like you tend to with polyester layers, or even like I have with the brand’s 175 Everyday Long Sleeve Half Zip Thermal Top on some particularly strenuous runs over the years.

Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top: features

Alongside the base layer’s ZoneKnit engineered panelling, the 260 ZoneKnit Long Sleeve Half Zip Thermal Top also comes with a handful of other features that I particularly enjoy. First, the thumb loops are a nice touch, making it particularly easy to hold the sleeves in place while you pull on mid, outer or shell layers. It also means that the sleeves stay put when you’re climbing or scrambling.

The three-quarter zip is of exceptional quality and comes with a nice friction detail on the toggle which makes it easy to grip and pull, even when wearing thin gloves. The zipper itself is also wonderfully smooth and has never snagged during all my time using this top.

For me, though, my favorite thing is the way this garment repels smells. Granted, this is something we should be thanking the sheep for, not Icebreaker, as this is a quality of Merino in general. But in all my weeks of using this top, I’ve only washed it a few times – wracking up a total of 10 runs and four hikes in it. Truth be told, I only washed it out of a sense of obligation rather than the smell telling me it was time for a cleansing, and I could probably have waited longer than I did.

Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top: fit

The fit of the Icebreaker 260 ZoneKnit Long Sleeve Half Zip Thermal Top is as you’d expect for a base layer: it’s tight, but not too tight that it’s uncomfortable. Naturally, for me, I’d never wear this thing solely as an outer layer, always opting for at least a baggier running top over the top of it. But if you’re body-positive and are happy with the way you look in skin-tight garments, then this is also a great-looking base layer that you could comfortably get away with at camp, après ski, or wherever it feels appropriate.

Overall, I love the 260 ZoneKnit Long Sleeve Half Zip Thermal Top. To me, it’s hands down the best base layer I’ve ever tried, and I’ll certainly continue to wear it on most adventures between late fall and early spring.

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