Review: Klättermusen Sigyn Zip Hooded Fleece

The biodegradable lightweight alpine fleece

Feature type Review

Read time 6 mins

Published Jun 15, 2023

Jonathan Doyle Jonathan is a freelance filmmaker, photographer, and drone pilot, based in the North West of England. His passion is for capturing real adventure stories about real people, the kind we can all connect with. Exploring connections with health, friendships and the environment by documenting the experiences of people pushing their limits, Jonathan brings their stories to life.

Our Verdict

Designed for alpine use, the Sigyn fleece from Klättermusen is a completely biodegradable, lightweight, warm and flexible active mid-layer with a distinctively designed asymmetrical front zip. 

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RRP £189
Weight 322g
Features Naturally antibacterial, fully biodegradable mateirals


  • Absolutely no micro-plastics released into the environment
  • Lightweight, only 322g
  • Asymmetrical zip avoids uncomfortable bunching at the chin


  • Comparatively expensive
  • Shorter body length than I would personally like


When I am choosing a mid-layer, warmth, comfort and weight are always at the forefront of my mind. I chose the Sigyn (pronounced Seeg-in) to test and review because I wanted a layer that was both warm and light that I knew would keep me comfortable out on a cool active summer evening.

What drew my attention most however was the fact it’s biodegradable and 100% plastic free. I was most curious as to how these materials have progressed and whether in reality they are a worthwhile investment.

First Impressions

I loved the colour of the Sigyn the moment I pulled it out of the packaging. The range follows a more earthy palette and the yellow in particular has a warm natural tone that is much more pleasing than the luminous colours other brands lean towards.

The texture is reminiscent of microfibre, softer than a standard synthetic fleece, but slightly more clingy.  

The Test

The test was a simple one; wear it every day for a couple of weeks in a variety of situations. I wore it on a couple of breezy days where I was stood fairly statically and in the shade for extended periods of time. I’d pack it down into a small bag and take it as a spare layer when climbing. While I didn’t take it cycling, I did get bike oil on the sleeve which was easy enough to clean off with a touch of washing up liquid. I also wore the Sigyn while talking my dog for her morning stroll.

The first day I wore it was while looking around the Freshwater Pearl Mussel Ark near Windermere. It was an overcast and windy day and I have to say I was cold. I was immediately concerned that perhaps the biodegradable material was just a gimmick, but after a quick comment, I found that the other people on the tour were just as cold in their ‘mainstream’ mid-layers. Phew.

Klättermusen describe the Sigyn as an active layer, meaning it performs best when the wearer is moving and generating body heat – not what I was doing on day one. From here on I wore it pretty much every day, often alternating between that and a Mountain Equipment waffle-style micro-fibre fleece for comparison. I am really pleased to report that I didn’t notice much, if any temperature difference between the two fleece materials, so a really positive result.

The test was a simple one; wear it every day for a couple of weeks in a variety of situations 


The Sigyn is for the environmentally concerned person who has a reasonable disposable income. It would be ideal for a slightly shorter person who is in need of a lightweight and comfortable mid-layer for use on cool summer evenings while participating in activities such as skiing, climbing and hiking.

What Stands Out


The innovative choice of material is a big plus for me. Brands investing in research and developing new plastic free materials should be higher on the agenda for most, and so it is great to see Klättermusen leading the charge.

Diagonal Zip

The asymmetrical (Klättermusen describe it as slanted) front zip is a feature I never knew I needed. I was skeptical at first, as we often are with change, but I have to say I love it. No more beard hairs being caught in the zip, no more zip curling into your chin and no more awkward bunching up.

Internal pocket

I actually really like the additional of internal zip pocket within the right hand pocket. It’s a smart solution to the dilemma of how to take a phone on a climb without it getting in the way or risking being dropped. It tucks under the waist loop of a harness so doesn’t restrict your leg movement and also helps to stop the fleece from riding up out of the harness. Good work Klättermusen.


The one design aspect I think could be improved upon is the general length of the jacket. I prefer a longer fit, with it covering a third to a half of my butt to ensure no accidental draughty spots are created. I find that the Sigyn tends to sit no more than a couple of inches below the top of my hip.


For £189 (at the time of writing), I would want an exceptional piece of clothing, and the Sigyn isn’t too far off. It has some fantastic features and the fact it is made of such future-thinking material definitely carries a lot of value. 

BASE Bottom Line

I didn’t really know what to expect with the Sigyn given that I’ve only ever worn micro-plastic shedding micro-fibre fleeces before. It’s all well and good being environmentally friendly and 100% biodegradable (except the zips), but how does it actually perform and for how long?

One characteristic to note about the starch-derived material is that it is not very stretchy, this might have some implications for the fit on people with larger frames. Furthermore I would say that due to the shorter body-length, the Sigyn would be more suited to shorter people if they prefer a longer fit like myself.

Overall I’m really happy with the Sigyn fleece. It’s warm when you need it to be, packs small when you want to travel fast and light, and will leave no trace when it’s time to be retired. I am curious as to what kind of lifespan this material has and what its relative carbon cost is compared to micro-fibre fleeces. Innovation like this is a huge step forward in responsible outdoor clothing production and hopefully will set a president for other brands to follow.

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