Osprey Mutant 38 Pack Review

© Toby Archer

The Mutant 38 is a technical rucksack with an emphasis on alpine and winter. It's not just for lugging your stuff to the crag; it's not a backpacking pack, or a nicely air-cooled walkers' pack: the Mutant 38 is designed from the ground up for climbers, and if you use it for much else, you'll sort of be missing the point. By extension, this makes it great for scrambling too. Of course a rucksack is a rucksack, and the Mutant is a well-designed and comfy one, so I have taken weekend backpacking gear in it and used it on walks too - but its features are very much focused on climbing.

It's a solid and well-featured mountain pack, and a good size for day trips  © Simon Watchman
It's a solid and well-featured mountain pack, and a good size for day trips
© Simon Watchman

I've owned a number of Osprey packs over the years, including a great one from the mid-noughties Aether range, a climbers' pack that I used for most of my ice and winter climbing for years. Generally I've found Osprey packs to be excellent value for money; that's not the same as cheap, but they have proved hard wearing, they come with loads of usable features and they are generally still quite light. At a very fair 1.28kg the Mutant 38 continues that tradition. Its RRP of £130 is far from unreasonable but it should be noted that there is serious competition at or around that price from the likes Patagonia, Blue Ice, Deuter and Mountain Equipment, with Arcteryx and Crux offering alternatives not substantially more expensive. So the Mutant 38 isn't going to sell on price alone, it needs to do its job well too. In brief: I have found that it does work rather well but after some use in pretty extreme conditions I have one reservation, which of all things comes down to Osprey's choice of colour!

Mutant 38 front view

Mutant 38 back view

The basics

The Mutant 38 is top-loading, single compartment, fixed back-system alpine pack. It has a removable lid with one main pocket and a smaller second zip pocket. Its nylon fabric feels tough for its weight, and sheds the snow well.


This unisex model has a fixed back length, and comes in two sizes, S/M or M/L. The back system is stiffened and made of relatively smooth snow-shedding material. The shoulder straps are contoured, firm and well cut; they work well when load carrying but do not restrict your arms at all when climbing. The fixed waist belt has some padding over the hips and helps in carrying heavier loads. Being fixed, it would completely obscure harness loops if used when climbing. There are a couple of gear loops on the padded section, but I've found it much better to double the waist belt up around the body of the pack when climbing - there is a loop to pass the belt through near the base of the pack designed for this.

Hipbelt folds back, for clutter-free climbing  © Oliver Prodhan
Hipbelt folds back, for clutter-free climbing
© Oliver Prodhan


The Mutant has lots of climber-specific features: the easy-to-use ice tool attachments fit everything from a straight walking axe to my pair of curvy DMM Switch tools. I could detach and re-attach tools wearing heavy, ice gloved in a screaming blizzard without too much faff. Gone are the z-compression straps of previous generations of Mutant; there are now just two straps, which makes for a much less cluttered-feeling pack. These straps are just long enough to fit a bulky Ridgerest or Z-Rest (although it's a bit of a fight). The straps also have little elastic tabs to stop the excess flying around - a nice touch.

The top compression straps on each side are closed by buckles and this works with a thicker strap near the base of the pack to carry skis in the A-frame style. They are wide enough to fit my bizarre, Michigan-made plastic ski-snowshoe thingies, so should fit even the fattest of powder skis. Daisychains down the front of the pack mean you could easily add elastic to carry a sleeping pad should you wish. The haul loop at the top of the back is stiffened, making it easy to grab, and it works excellently as a clip in point to hang at belays. There are two further little stiffened loops near the top, and this means you can haul the pack with a three point attachment. I've not needed to haul the Mutant yet, but having a three point attachment makes the pack hang straight and it will snag much less readily.

The mesh helmet carrier is a nice touch but not realised perfectly. Deploying it from where it is attached in the second zip pocket in the lid, it's not really clear where you attach the little clips to hold down the front. There is thin webbing daisy chain on the lid and there are also stiffened loops that are part of the hauling system - but these options either seem to be too far away or too close depending on how full the pack is. One possible hack is to detach the helmet carrier from the top pocket (allowing you to use the pocket again), attach it to the ice tool holders and with the helmet in it, clip the clips into the daisy chains above the tool holders. This works really well although the Osprey logo is then upside down making me think the designers hadn't thought of it! Alternatively I've found with the decent capacity that I often just pack my helmet inside.

Osprey tell us that the helmet net has now been changed from a zip attachment to a Velcro attachment and the toggles changed to hooks to make it easier to deploy and affix. They say the net can also be attached to the front daisy chains.

Snow shedding back panel and big haul loop that makes a great clip in point
© Toby Archer

Lid pocket removed for a lighter, smaller pack
© Toby Archer


For its stated 38 litre capacity, the Mutant feels quite roomy. The pack swallows full winter climbing kit - half a rack, a rope, crampons, helmet, belay jacket, extra layers, flask and so on. It also easily fits weekend backpacking gear along with a helmet when I'm going scrambling on my own.

The pack is available in two sizes; S/M and M/L. My Mutant was a pre-production sample, so I suspect it is the M/L size. This means plenty of capacity in the pack, but rock climbing with it a few times, even when it's virtually empty, I've found the stiffened back bumps into my helmet when I'm looking up. This is odd because I do not remember this as an issue at all when climbing winter routes. Perhaps in summer, wanting to be able to use a chalk bag, I did the shoulder straps up slightly tighter when climbing, holding the pack higher up my back. The back stiffener (a plastic sheet with two aluminium staves attached) is easily removable but then the pack doesn't carry loads so well.

The other big design feature for climbers is that the top lid is easily and quickly removable for stripped-back climbing days. Osprey have cunningly added a secondary flap with buckles on it. This tucks away almost unnoticed, but can be pulled out and over the drawcord opening on the pack if you have removed the lid. This stops snow accumulating there, an issue on some other lidless designs. Owners of the previous version of the Mutant will already be familiar with this feature, and it's good news that Osprey have kept it. There is also a rope holding strap under the lid, that can be used regardless of whether the lid is on or not.

Welsh ice with the Mutant 38  © Oliver Prodhan
Welsh ice with the Mutant 38
© Oliver Prodhan

Helmet holder in use  © Toby Archer
Helmet holder in use
© Toby Archer

Any issues?

So why isn't this the perfect climbers pack? Simply, the colour choice that Osprey have made (black with black features, or dark blue with dark blue features) makes it surprisingly hard to use all those features on a grey, overcast winter's day, let alone at night.

On my pre-production sample all the straps and buckles are thin and black, which set against the black fabric of the pack makes them very hard to use. On the production version Osprey have made the side compression straps a contrasting light blue, but all the other features remain black. My sample is what Osprey call the "Black Ice" colour scheme; there is another option: "Blue Fire" - this may be a little better but still the straps and buckles are the same colour as the pack body.

The pack arrived for testing just days before we woke in Sheffield to the dump of snow that was "the Beast from East". As a teacher I was greatly disappointed to find out that morning that the snow had closed most of the schools in the area, including my own. To get over this disappointment I teamed up with a friend, also a teacher with an unexpected day off, and battled through the snow to Edale. We followed the Pennine Way up onto the Kinder plateau and into some of the worst weather I've experienced in over 25 years of mountaineering. Dropping down Red Brook to contour round to Kinder Downfall we escaped from the wind to some degree, but found ourselves floundering around in deep powder.

The climb was dispatched quite easily, but the walk back along the Pennine Way took careful navigation, all our mustered experience and some mental fortitude. Thick, insulated gloves were needed to keep hands warm, but those gloves also were too clumsy to do things like set a compass bearing or do many things with the rucksack. But taking a glove off was actually scary: the wind-speed meant very quickly your fingers would become unusable. Here the pack's colour scheme was a real problem, so dark inside it was hard to find what I needed.

Yes, I was wearing goggles, ice encrusted thick gloves, and it was a screaming blizzard with about five metres of visibility, but that is when these seemingly minor issues become much more serious ones. That afternoon I only lost a crampon bag that escaped while I was trying to get my walking poles out of the pack and attach my ice tools to it, but there were some expletives used as I struggled to open and close the pack, trying to find a black buckle, on a black strap against a black pack in low light. Losing a glove in such conditions would be serious, so having to take one off to fiddle with rucksack straps really brought this issue home. Subsequent times using the pack in slightly less extreme conditions, but still typical British winter - grey and overcast, often in cloud or heavy snow - reinforced this is a real issue.


Overall, this is a comfortable, reasonably light alpine sack, packed with features that are useful to climbers, and at a competitive price. It's a shame that the colour scheme is something of a drawback. I can only think that the decision to go with matching colours was an aesthetic choice, and whilst the pack may look smart on a summer day, I don't think it was the right call for a winter climber's pack. The Mutant 38 works well in so many ways but if you are a UK winter climber I would definitely go for the lighter colour scheme and be aware that in poor conditions the pack becomes more fiddly to use than, arguably, it needs to be. Perhaps next year Osprey can add more contrasting straps and buckles, but otherwise keep the pack unchanged? Then I think they would be onto a real winner.

Osprey say:

5th generation of Mutant is a reliable, intelligently-featured climbing pack for year-round ascents. Super light, flexible, strippable and seasonally versatile, you can rely on this perennial climbing partner. When making cold-weather ascents, you'll appreciate the snow-shedding fabric backpanel, side ski carry loops and dual ToolLock™ system which allows quick and secure ice axe attachment. The main entry to the Mutant 38 is through a floating and removable top lid, which means you can overload your pack like a packhorse or remove the lid totally for greater head clearance and lighter weight. Lesser climbing packs have minimal weather protection and compression when in this mode, but not the Mutant 38. Use the built-in FlapJacket ™ that provides weatherproof closure; it keeps your gear fully compressed.

  • Dual front daisychains
  • Dual ToolLock™ for ice axe attachment
  • FlapJacket™ top cover for use without lid
  • Glove friendly buckles
  • Gear loops on hipbelt
  • Integrated ski/climbing helmet storage
  • Internal hydration sleeve
  • Key clip
  • Internal top load compression strap
  • Reinforced 3-point haul system
  • Reinforced base
  • Removable HDPE framesheet with T6061 aluminium stay
  • Sewn in hipbelt, reverse wrap stowable
  • Side ski carry
  • Snow-shedding fabric backpanel
  • Sternum strap with emergency whistle
  • Top lid access

  • Price: £130
  • Sizes: S/M or M/L
  • Weight: 1.28kg (M/L)

For more info see

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16 Oct, 2018

Hi Toby,

A climbing pack should be designed to work when actually climbing, otherwise it's just a pack.

Why does any climbing pack have a padded waistbelt, that interferes with harness? In the case of this one, wraps around back, allowing it to catch on other stuff, gear, etc!

The colour is also not user friendly and it weighs too much. Less is more.....


19 Oct, 2018

Absolutely agree on the colour comments. I scored a Mutant 38 for £55 in a sale, yet assessing it seriously I returned it on the basis of shoulder strap comfort and colour. Black simply makes sacks difficult to work with - regardless of other virtues. Manufacturers please take note. In the end I went with a white Lowe Alpine Ascent Superlight. A much fewer featured sack, but all useable.

20 Oct, 2018

Interesting, i've found it carries rather well. What didn't work with the shoulder straps for you?

20 Oct, 2018

I found the width of the shoulder straps over my shoulder a bit intrusive and restrictive for me between deltoid and collar bone. ( I'm 6', 42" chest). I found the same with the straps on a Blue Ice Warthog 40 - they cut the circulation to my arms a bit. I get on better with narrower, less padded straps like the LA Superlight, or older less cushioned designs. Even the latter LA Mountain/Alpine Attack models where the foam extends round the inner edge of the strap put me off. My ideal would probably be the double stranded thin strap system of the Cilao packs ( tho I haven't tried them yet.)

20 Oct, 2018

Me too. I got one of these a few weeks ago to replace an original Mutant 38 which had been a collateral loss when my car got nicked. The original had handled 7 years of abuse in mountain rescue and I was devastated not just by the the loss of the sack and its contents, but that I wouldn't get a replacement exactly the same. Good news is that I already love this version of the Mutant, it fits me extremely well (but that's like boots, isn't it - an element of pot luck re: body shape and sack design). What I haven't had to deal with yet is fiddling with the straps in cr@p conditions - it'll be interesting to see if I agree with the criticisms that have been made regarding lack of contrast in colours.

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