Thermowave Merino Xtreme Baselayer Review

The Thermowave Merino Xtreme is a long-sleeved, high necked baselayer which uses a combination of polyester and merino wool to keep you warm without feeling itchy on your skin. Is it the best of both worlds?

Thermowave is a Lithuanian brand who have been making clothing for 85 years. They've been recently brought to the UK market for the first time by their distributor, First Ascent.

The Merino Xtreme certainly allows freedom of movement. It might have lifted a bit here but I am jumping!  © UKC Gear
The Merino Xtreme certainly allows freedom of movement. It might have lifted a bit here but I am jumping!
© UKC Gear


I've worn the Merino Xtreme over the winter for a variety of activites from snowy walking in the Lake District to chilly bouldering (and believe you and me, standing around bouldering when it's 0° and windy is when it gets really cold...). The Merino Xtreme is very warm for a baselayer and I've found that the fabric is not at all itchy or irritating on my skin.

The inside of the baselayer is made of 100% polyester, which is why it isn't itchy like many merino wool baselayers can be. And being polyester, it dries quickly so the moisture from your skin wicks away. The outside is a blend of 80% merino wool and 20% polyester, which keeps you warm and is breathable. Being a blend of natural and synthetic fibres, I have also found that, unlike many merino baselayers, the Merino Xtreme hasn't shrunk after I've washed it, and neither has it got baggy and lost its shape. The polyester component seems to add durability to the fabric. Meanwhile, the wool has a big advantage of its own - unlike 100% synthetic fabric, it is not prone to getting smelly. All in all the synthetic/wool blend of the Merino Xtreme works really well, offering you the best of both materials in one. Because it's not itchy whilst also being warm, I'd highly recommend it, and I would certainly choose other baselayers made of this material in future.

It is worth noting that Thermowave's merino is certified 100% mulesing free (mulesing is a pretty nasty practise, and an animal welfare issue that's particularly relevant to merino sheep).


The cut of the Merino Xtreme is undeniably odd - so much so that the original reviewer lined up to cover it had to pass it on to me (I'm skinnier). I've been wearing a size large and, at 6 foot with a slim build, the Merino Xtreme is extremely tight on the chest and extremely long in the body on me. It feels a bit odd when you put it on and it certainly looks a bit odd too. Sometimes when clothing is cut in a specific way you think 'ah, ok it's for someone of that body type' but I don't think I've ever seen anyone who looks like that!

Great as a single layer once you start to get warm
© UKC Gear

That said when you're wearing the Merino Xtreme you don't actually notice the cut being odd - it doesn't actually feel too tight across the chest as the material is quite stretchy and being long in the body is quite nice as it provides lots of coverage over your bum and keeps the wind out. It's also good for tucking into your trousers. It also means that when you're lifting your arms above your head - climbing for example - the hem never lifts above your waist. This would also be good for skiing so that when you fall over you don't get snow up your back. As the material is quite stretchy the Merino Xtreme is also great for climbing in, as it's not at all restrictive - you can easily move your arms around whilst wearing it.

Oddly tight on the chest...  © UKC Gear
Oddly tight on the chest...
© UKC Gear

... and oddly long in the body  © UKC Gear
... and oddly long in the body
© UKC Gear


Being a baselayer the Merino Xtreme is understandably short on features; however the zip and collar are worth a mention. The chest-length zip is always nice on a baselayer as it's one of those pieces you often wear when you start out cold and soon get warm, hence it's nice to have a bit of ventilation. The high neck is also good for an extra bit of warmth and to stop the wind going down your collar. Neither the collar nor the zip are scratchy or irritating, which is definitely a plus!

The zip is a nice feature for extra ventialtion  © UKC Gear
The zip is a nice feature for extra ventialtion
© UKC Gear


I think the Merino Xtreme is a great baselayer due to its warm, comfortable and stretchy combination of merino wool and polyester. Although the cut looks a bit odd, and it definitely won't fit every user, in practice on me it works well for climbing and other activities as it allows free movement and doesn't lift above the waist. I would certainly choose more baselayers made of this material, as there's nothing worse than an itchy baselayer - except, perhaps, a smelly one! Pants in this material are also available; but we won't subject you to those pictures...

Thermowave say:

Thermowave's Merino Xtreme - an advanced dual layer with a combination of Merino wool and Polyester for bravers who seek out the best properties of both fibers. Inside polyester is designed for optimal moisture management, while outside Merino wool has supreme insulating properties and is naturally anti-bacterial.

  • Sizes: S-XXL (men) XS-XL (women)
  • Dual-layer fabric that ensures best properties of both merino wool and polyester
  • Composition: 80% Merino wool and 20% functional polyester (outside), 100% functional polyester (inside).
  • Ensure perfect warmth insulation
  • Optimal moisture management
  • Excellent for the colder conditions
  • Natural anti-bacterial protection
  • Suggested activity: running, mountaineering, outdoor and snow sports.

For more info see

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4 Mar, 2019

Is this mulesed (and certified as such) or non-mulesed merino?

Good question Graham, I'll ask

We've had a quick response: Thermowave are certified 100% mulesing free

I looked up what mulesing actually is. It's not nice

5 Mar, 2019

No, its not nice. And not necessary either.

I had a quick scan of their website to try and find the answer before posting my question. I couldn't see any reference to their sourcing of wool and it seems odd not to include this info somewhere - surely it would only ever be taken in a positive light? If you've got something to differentiate yourself from the less ethical merino stuff on the market then why wouldn't you ? They're not alone in missing a trick though.

7 Mar, 2019

As with many things, I'm not so sure it's as black and white as that:

As long as the sheep are anaesthetised, surely mulesing is a resonable response to control fly strike (which is horrible and can be deadly)? (I realise we're very far from hiking subjects here!)

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