Osprey Nimsdai Mutant 90 Pack Review

Osprey Nimsdai Mutant 90 Review

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The Nimsdai Mutant 90 is an exceptionally well featured and surprisingly versatile large mountaineering pack that carries like a dream.

The Osprey Nimsdai Mutant 90 is a rare beast in many ways. Designed with input and testing from Nimsdai Purja to be the ultimate high altitude mountaineering pack it is unusual to see such specialist kit made generally available – more often such items are limited runs done by the prototype departments (often nicknamed Skunkworks after Lockheed’s ADP department) of big manufacturers or produced by small custom builders. The fact that Osprey have made the Mutant 90 a mainstream product perhaps reflects that the pack is a lot more versatile than you might expect given its origins. The pack went through three major prototype stages with earlier versions used on the first winter ascent of K2 as well as Everest and it is difficult to imagine a large capacity high altitude pack with better credentials.

I tested the S/M version at a volume of 88L and a weight 2kg. As with the vast majority of Osprey’s product range there is a strong emphasis on the environment and the Mutant 90 uses a bluesign® approved 210D recycled nylon grid NanoFly fabric with a PFC/PFAS-free DWR. The fabrics have been chosen to optimise snow shedding and a sensible weight balanced against durability. Osprey’s construction quality is well known but to give a little perspective Osprey receive only 0.04% returns on their packs.

Like its smaller siblings in the Mutant range the Mutant 90 has been designed to be versatile and strippable. The lid is removable and includes a stash-able stretch mesh helmet holder. The cavernous lid pocket will accommodate pretty much any ‘need on the hill’ kit, just to see I got 5 X 1 litre Nalgene bottles, hat, gloves, first aid kit, map and compass in with plenty of room left over! Should you choose to forego the lid there is a generous snow skirt to seal up the lidless pack and Osprey’s ‘FlapJacket’, a flap that has Fastex buckles to attach to the lid straps to further weather seal the lidless pack. The lid itself has an under-lid rope attachment which fastens with a fixed ladder lock buckle necessitating the ‘threading’ of the rope through which seems a little odd. When you open the lid the rope flops with it out of the way of pack opening which has its pros and cons. On the plus side you get unencumbered access to the body of the pack when you open the lid but the negative side is the rope does flop around and you need to make sure the strap is snug or it will slide out. As you would expect on a mountain pack the main body is one huge compartment. There are a couple of red load tension straps to pull the top of the main body inward to stabilise massive loads should you ever manage to fill the pack, something that would only seem likely for wilderness or high altitude guides!

Externally there are two over sized ‘wand’ pockets for snow-stakes etc. each are large enough to accommodate an oxygen bottle such as Summit Oxygen or Poisk if required. There is also a semi rigid ‘shield pocket’ panel on the front of the pack that does dual duty for retaining the heads of your ice tools, crampons or any other pointy extras such as snow shoes etc. and could certainly be used to rapidly stash a frozen flysheet when trying to make an early morning exit from camp. Together with the side compression straps this panel also allows the pack to be compressed down to a much more reasonable size very reminiscent of Osprey’s classic ‘StraightJacket’ foam panel compression system. Below the side compression straps there are also two reinforced ski carry loops. The hip-belt is adjustable vertically through a simple velcro system passing behind a padded lumbar pad so you can fine tune the fit of the pack to a limited extent within each of the two sizes and the hip-belt itself comes fitted with gear loops. One final feature of the pack are the reinforced loops for potentially attaching a pulk for those Polar or Greenland crossing treks or lashing ridiculously bulky items (ladders?) to the pack – I’m unsure if these are strong enough for a pulk attachment (and why not just stick your pack load in the pulk?) but will find out and update the review accordingly. The huge carrying capacity has intrinsic advantages for winter and high altitude climbing in that you don’t have to carefully pack your kit when befuddled by cold, altitude and exhaustion – with a pack like the Mutant 90 you can haphazardly just stuff in that bulky sleeping bag and other items.

A 90 litre mountaineering focussed pack will live or die by the quality of its carry, if it’s uncomfortable or unstable then it is not going to cut it. Osprey have a solid reputation for comfortable backpacking packs and that know how has obviously fed into the design of the Mutant 90. Whilst the Mutant 90 lacks the sophistication (and complication) of the Fit-on-the-Fly harness of something like the Atmos AG 65 the simple 4 mm LightWire frame transfers the load effectively to the hips and the harness system keeps things close to your centre of gravity making for a very stable carry. Carrying heavy loads is never going to be fun, the muscular workload and the pressure from a pack harness on shoulders and hips is usually something to be endured. The Mutant 90 can’t do anything about muscular workload (that’s just down to fitness and putting the training in) but the harness system distributes the weight perfectly making loads feel ‘lighter’ and more stable allowing you to traverse rough ground stumble free. To someone like me who tends towards minimalist packs for climbing and feels that a 40 litre pack is ‘big’, hiking into a bothy with the Mutant 90 full of logs plus usual winter kit was an almost pleasant surprise. There was no getting away from the weight but there were no pressure points on either hips or shoulders. The packs design meant the load was kept close to my centre of gravity so there was no sway to unbalance me on rough ground. Once the logs had been delivered I could detach and stow the lid (after consuming the generous second breakfast it contained) cinch down the Mutant 90 and deploy the FlapJacket for an easier hike back to the van. On the hike out if you had told me I was carrying a 40litre pack I would have believed you, in its stripped and compressed form it carries like a much smaller pack and is surprisingly unobtrusive, relatively speaking. Would I carry the Mutant 90 for technical winter climbing in Scotland? Probably not as a first choice, but I’d be happy with it up to Grade 4 or 5. However the fact that it carries so well and can be compressed so effectively got me thinking about normal climbing and hiking scenarios where it would be useful. Firstly the typical CIC trip: you need a ton of food plus whisky at the hut but once there you can climb with a light day pack on the Ben. So pack in with the Mutant 90 and then tackle up at the hut and climb with a day pack you stuffed into the Mutant 90 or with the compressed Mutant 90 itself. All that extra whisky will make you friends in the evening… Secondly: big alpine days involving an initial bivi or multiple routes from a ‘basecamp’ bivi/camp. Similar to the Scottish scenario permitting a more luxurious camp/bivi with the stripped/compressed Mutant 90 being used on route. Finally: disparate partners, perhaps parent and child or big lad small lad, I’ve long argued that rack weights should be divvied up based on a percentage of body weight, strangely none of my big mates will listen… The Mutant 90 allows one partner to take a larger share, again especially useful if we are talking about food and water on the first day of a multi day endeavour. Obviously there is then the Mutant 90’s raison d’être: high, remote mountaineering whether that be Alaska, Greenland or some Himalayan peak. Beyond documentaries and books I have no knowledge of these activities so I can’t comment further but he pack’s feature set has quite literally been tailor made for these activities!

Overall I’ve been extremely impressed with the Nimsdai Mutant 90. I’ve not used it for any winter climbing but I will to see how it fares and I’ll update the review. When we were first offered the pack for review I was intrigued that Osprey should bring to market what looked to be an avowedly hyper specialised piece of kit. Surely the market for such a pack would be too limited? However using it for these last few months in the relatively tame terrain of an autumnal and winter UK I can see that it more versatile than I at first thought and as a consequence may have far wider market appeal. It is still an awesome piece of specialist kit but it’s not purely destined for use by Himalayan mountaineers.


  • Capacity, stability and comfort
  • Compressibilty
  • Build quality
  • Specialised targeted feature set
  • Surprisingly versatile


  • Odd rope strap
  • It’s BIG!

SRP £275


Disclaimer – CGR reviewers are never paid to provide a review and the website does not take advertising. We are a bunch of keen climbers and travellers that accept sample products and offer an honest and independent review of the item. The reviewer will often keep the sample after reviewing it for both hygiene reasons and more often they’re in no fit state to return!


  1. Hey there. I’m looking into buying this pack. My may concern is, as I must bring it back inside my luggage, what is the actual size of the rigid part, as that is what i will actually need to fit inside my luggage with the pack empty.

    1. Hi tomasfd I measure my s/m at 23 1/2″ or 60cm for the rigid wire frame. Apologies for the delay in replying as I’ve been away in Norway. Let me know if you have any other questions.

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