Jöttnar Uller Yak Wool Base Layer | Review

One of the best winter baser layers we've used, desgined with a blend of Tibetan yak wool and polyester.


The Jöttnar Uller Yak Wool Base Layer’s name is arguably slightly deceptive, it’s actually made from a blend of Tibetan yak wool and polyester, but whatever the fine details, the end result is one of the best – if not the best – winter weight base layer tops we’ve ever used.

For starters, the thick, winter-weight, fabric is amazingly soft and luxuriously comfortable against the skin. It is genuinely a pleasure to pull it on, a bit like sliding under a warm duvet on a cold, winter’s night.

Meanwhile the cut is sleek and close but not tight, helped by a little bit of stretch in the fabric. It’s decently long too with a bit of a drop to the tail, which helps avoid cold spots at the base of the back due to the top rising up.

All Your Base Is Belong To Us

All the basics are covered too. The seams are flat locked for minimal chafing, the shoulders are seam free to maximise comfort when wearing a pack and the neck label is a non-scratchy, soft, PU one.

It uses a versatile format – the deep quarter zip-neck allows rapid venting and the stand-up, double thickness collar adds comfort, warmth and protective the back of the neck from the sun.

All of which is great, but not exactly unusual. What really impressed us is just how well that fabric performs. It’s made using a blend of 67% polyester and 33% yak wool. Apparently the latter is sourced from free-ranging Tibetan yaks living at an altitude of around 4,700m – gasp – and temperatures ranging from -28°C to +21°C.

The wool is obtained by combing the yaks’ coats and the stuff Jöttnar use is the ‘thinner softer hair that is shed in the spring’ which gives the Uller its softness.

Seven Day Test

We agreed with Jöttnar that we’d wear the top for seven consecutive days and that’s pretty much what we did with impressive results. The thick, soft fabric turns out to be not only super soft and comfortable, but also to handle moisture and heavy sweating deceptively well.

We say ‘deceptively’ because we weren’t expecting a thickish fabric to cope with really intense use. Where merino wool, for example, tends to degenerate into a soggy state after a certain point, the yak wool blend, just seemed to keep coming back for more and when it does get damp, it stays comfortable.

It’s great for general walking and even running use in cold conditions, but we were amazed how well it stood up to a brutal interval session on an indoor stationary bike.

On top of that, it dries impressively fast and doesn’t seem to hold odours to any significant degree. We don’t know whether there’s some sort of anti-microbial treatment in addition to the yak wool component, but whatever’s going on, it works.

Yes, at the end of the seven days of solid use, there was a slight, up-close whiff to the arm-pits, but the top was still completely wearable in polite company.

Other stuff we liked includes the subtle, colour-contrasting stitching, the protective flap behind the main-zip and the small, but handy chest pocket. Great for stashing small objects if you’re using the top as an outer layer. And aesthetically, the embroidered Jöttnar logo looks neat.

The only negative we’ve noticed is some very minor bobbling at the top of the collar, presumably from rubbing against outer layers plus at a measured 286g for a medium, it’s not the lightest option out there.


Excellent, super soft and comfortable winter-weight baselayer top that’s nicely designed and made. What impressed us most is that despite being a relatively thick fabric, it still manages to deal effortlessly with moisture, dries decently fast and resists odour as well as anything we’ve used.

Simply an deal cold weather mountaineering or general outdoor base layer that shrugs off multi-day use. Yes, it is expensive, but it works very well indeed.


Soft, rapid wicking and drying, nicely made, stretch fabric, neat fit, handy chest pocket, deep zip and protective collar.


Not the cheapest or lightest.

Performance: 5.0
Reliability: 5.0
Value: 4.5

More info:

Full specs

  • Price: £90.00
  • Year: from 2015
  • Weight: 286g
  • 33% Yak Wool / 67% Polyester
  • Flat-locked seams throughout
  • Seam-free shoulder-tops
  • Double thickness collar
  • Deep venting zip
  • Soft PU neck label for comfort


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