Osprey Mutant 38 Backpack Review

Osprey Mutant 38 Backpack
Osprey Mutant 38 Backpack

Designed for climbing and winter peakbagging, the Osprey Mutant 38 Backpack only weighs 2 pounds 15 ounces (size medium), and has a clean streamlined design optimized for rock and ice climbing that won’t slow you down over rough scrambling or more technical routes.

Key Features

  • Dual ice axe/tool attachments (top and bottom)
  • Climbing rack loops on hip belt
  • Z compression straps
  • Top compression strap and rope carry
  • Removable tri-fold bivi pad
  • Removable framesheet
  • Removable/floating lid top pockets
  • 3 point haul system
  • Spindrift collar
  • Dual snow picket/avalanche probe pockets
  • Load lifters
  • Adjustable sternum strap with emergency whistle buckle
  • Fixed Ergopull hip belt with reverse wrap capability when wearing a climbing harness
  • Padded shoulder straps with elastic keeper straps
  • Hydration reservoir pocket and left/right hydration ports

Suspension System

The Mutant is primarily a winter climbing or snowsport pack. You can tell this immediately by looking at the backpad on the pack which is made out of thermo-molded EVA foam. It doesn’t have much in the way of ventilation because in winter you want your backpack to mold around your back and provide you with additional insulation.

The other thing about this backpad is that it’s annealed directly to the main compartment of the pack without any kind of gap between the two. This keeps the center of gravity of the pack very close to your back so it feels like it’s an extension of your body and moves when you do. This is the exactly kind of fit you want for climbing, scrambling or mountaineering to avoid burning out your muscles on vertical ascents.

Internal Suspension Components - Bivi Pad and Framesheet
Internal Suspension Components – Bivi Pad and Framesheet

The Mutant also comes with two additional internal suspension components: a bivi pad together with a plastic framesheet. Together they provide the EVA backpad with a little extra stiffness and help improve the transfer of weight from the main compartment to the hip belt. They also prevent the back of the pack from collapsing on itself when the main compartment is not packed tight, which would shorten the pack’s torso length and throw off its fit.

The bivi pad and the framesheet are optional and removable if you want to save a little pack weight, but you should only do this when the main compartment is packed tight and the EVA backpad can’t collapse on itself.

  • The plastic framesheet weighs 5.2 ounces.
  • The tri-fold bivi pad weighs 2.5 ounces and is 1.4 cm deep when folded together.

Design-wise, a plastic framesheet is a normal component in a pack of this size and this one does a great job in transferring the load to lumbar pad at the base of the backpad, which is sewn into the hip belt.

The bivi pad is rather unusual though and not something I’ve seen on the other Osprey packs I’ve reviewed in the past. In this pack, it’s primary use is as a shim to secure the plastic framesheet in place in its interior pocket and prevent it from buckling when the pack in not tightly loaded. It is not as useful as one might hope as a bivy pad under a sleeping bag because it’s only 24 inches long and barely reaches from my shoulders to my hips when I lie on top of it (I have a very short torso). It’s also way too thin to provide any cushion or thermal insulation and not something I’d recommend that anyone use for anything except a sit pad.

Mutant 38 Hipbelt
Mutant 38 Hipbelt

The Mutant’s hip belt is a significantly more functional and has some nice climber specific features. Like other Osprey packs, the Mutant uses an ErgoPull hip belt which I really like because you can get a tight and secure fit. The hip belt itself is not heavily padded nor does it have to be for the 30-ish pound loads that you are likely to carry with this pack.

If you are climbing and using a harness, the hip belt can be wrapped around the back of the pack and secured to keep it out of your way. There are also racking loops sewn into the hip belt that you can suspend gear from, though you’d probably use a real climbing rack or harness for anything serious.

Unfortunately, the hip belt only comes in fixed lengths corresponding to torso lengths and is not replaceable if you happen to be short, but say, have a large waistline. I hate it when manufacturers design packs like this, so be forewarned and make sure that you can get the fit you want before you set your heart on buying this pack. I wish more backpack manufacturers provided mix and match hip belts in different sizes with their packs, but unfortunately I expect hell will freeze over first.

Compression System and External Attachment Points

The Mutant has a minimal compression system that’s primarily intended for compression and not for strapping external gear to the outside of the pack. This makes sense when you consider that it is designed for specifically for technical climbing or rock scrambling.

Mutant 38 Compression System
Mutant 38 Compression System

What compression there is, is limited to a pair of  Z compression straps on the sides of pack which are designed to save weight but not to attach gear.

In addition, the pack has a  floating lid which can be used to sandwich gear between the top pocket and the main compartment. The floating lid is removable, potentially saving another 6.3 ounces of pack weight, but doing so would remove a considerable amount of storage space from the pack and is probably not worth doing.

Storage Capacity

The Mutant has 38 liters of storage space split between a main compartment and a floating lid, which has one external pocket and one internal pocket. There is an 8.5 inch spindrift collar at the top of the main compartment that you can stuff more gear into as well.

Large Main Compartment and Floating Lid
Large Main Compartment and Floating Lid

The only other external storage on the Mutant are a pair of snow picket sleeves on the sides of the pack.

The Mutant doesn’t have any side pockets for water bottles, but it does have an internal hydration pocket and dual hydration ports to let you run a hose to the shoulder straps. However, in testing the Mutant with a hydration bladder, I found that a full reservoir can be felt through the EVA backpad when the main compartment is stuffed tight, even when the plastic framesheet and bivi pad are in place.

Emptying the pack or drinking down the reservoir relieves the discomfort, but it makes packing the pack a little tricky if you have a lot of gear to carry and you need to carry a lot of water. I don’t use hydration reservoirs anymore because I’ve experienced too many leaks with them in the past, so my workaround is to simply carry water bottles on top of my other gear for easy accessibility.

Overall Recommendation

The Osprey Mutant 38 is an exceptionally comfortable backpack to carry with an excellent hip belt system and lumbar padding designed to transfer weight off of your shoulders and onto your hips. But it really is just intended for climbers or and not backpackers. If you are a rock or ice climber, and you like a form-fitting technical pack feels like it’s an extension of your body, this is the pack for you.


  • Extremely good weight to hip belt load transfer
  • Streamlined design, perfect for rock climbing and snow sports
  • Excellent compression system
  • Floating lid with spindrift collar


  • Full hydration reservoir can interfere with packing and fit
  • Hip belt is not replaceable, and is based on torso lemgth.
  • Bivi pad is too thin and short to be used under a sleeping bag

Disclosure: Osprey Packs provided SectionHiker.com with a Mutant 38 for this review. 

Editor's note: Help support this site by making your next gear purchase through one of the links above. Click a link, buy what you need, and the seller will contribute a portion of the purchase price to support SectionHiker's unsponsored gear reviews, articles, and hiking guides.

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  1. Superb review, thanks. I have one coming to test soon and it will, along with the Crux AK-37, be my alpine pack for the coming year. I'll alternate between the two to see which I prefer but it's a great pack but a little heavy for its volume – the Crux is 960g. How are the ice-axe loops in comparison to the red (older model) which are simply loops?

  2. i have and use the older mutant 38 …

    a few comments

    – i suspect the volume is much more than 38L … i have seen 50L packs with comparable volume

    – for heavy loads replace the plastic backpanel with 1mm pine board, the pack will then carry up to 40+ lbs with no frame collapse

    – the compression straps are the best ive seen yet, being a Z style … also they are meant to carry pickets or wants on the outside, thus the shallow pockets on the sides … also if the straps get wrecked they are not sewn on so are easily replaceable unlike some other packs … or you can replace it with rap webbing for those "oh shiet" situations

    – with some bungee cord you can easily rig up a carry system on the back for a shovel or misc things

    – the material is fairly durable, however i do not recommend any hauling except in emergencies despite the haul loops … ive got a hole or two in mine, repaired with duct tape and seam grip

    and best of all the pack comes with ospreys feed it to a bear and well fix it or replace it guarantee …

  3. Maz – Thanks – The ice axe system is well designed, particularly for people who don't know how to attach axes using traditional loops . The handles are held by top and bottom bungies and the picks slot into a reinforced patch at the bottom of the back of the pack. Despite probably adding a little weight, I think this is a good feature because it requires the picks to face in when worn, and prevent people from having one stick their hip if they fall.

  4. eric – I had that same feeling with my newer mutant – it feels a bit bigger than it is rated, although it still too small for an overnight. Good points about the z compression strap and the guarantee. I also tried rigging a carry system with thing elastic cord, but there are pitifully few external attachment points on the pack: none on top of the floating lid and the side ones are arranged poorly. I concluded that Osprey really wanted to make this a streamlined climbing pack for day climbing purists instead of one which has overnight capabilities. This is a strikingly different design attitude than their other products,btw, which try to cram multiple activity features onto each pack.

    I also tried using other materials for the framesheet but was too lazy to cut anything to fit the lumbar pad. It is doable though. We must be cut from the same cloth. :-) Thanks for the comment.

  5. Big fan of the Variant 37 (also have the 52). A little heavier than the Mutant but I found of easier to lash snowshows and crampons on it.

  6. I use the Mutant 38 as a day pack and an overnighter for backpacking. It fits quite well and has plenty of space for an overnight trip (except maybe in extreme cold). The primary reason I got this pack was for doing 14er’s and it shines in that department, I have done 2 already and soon heading to Barr trail to tackle that. Even when packed light for a summer day trip the compression straps will cinch the load down tight. I haven’t tried many other backpacks so I can’t say how this stacks up to other packs but I can say for what I do I couldn’t wish for anything more.

    • Another comment on you review. I use the 2 liter Osprey bladder in my pack. It has a stiff side that you put towards your back so there is no bulging against your back. If the water is running low I compress the pack further to maintain the stiffness that I prefer on a pack.

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