The Osprey Mutant 38 is a versatile alpine backpack that’s equally at home on winter hiking trails, ski mountaineering tours, or ice-climbing routes. It’s an internal frame pack that is loaded with external attachment points that make it easy to haul bulky gear from ice axes and rope to skis, crampons, and snowshoes, with strippable components that can be removed to save weight. Glove-friendly buckles, a snow-shedding back panel, and a harness-compatible, reversible hip belt make it a nimble and capable companion for all-day adventures in the mountains.
Specs at a glance
- Type: Internal Frame (removable)
- Access: Top, Floating lid
- Pockets: 3
- Mfg Weight: (S/M: 43.2 oz/1225 g; M/L: 44.8 oz/1270 g)
- Actual tested weight: (M/L: 42.8 oz / 1213g) – in other words, 2 oz under spec.
- Removable components: Top lid (4.5 oz), framesheet (6.0 oz), aluminum frame stays (2.8 oz), helmet carry net (1.5 oz)
- Load lifters: Yes
- Helmet carry net: Yes (top or front)
- 3 Point haul loops: Yes
- Reversible harness-compatible hipbelt: Yes
- Hipbelt gear loops: Yes
- Hydration compatible: Yes
- Ice tool holders: 2
- Ski carry: Reinforced A-frame straps
- Torso range: (S/M: 15-18 inches; M/L: 18-21 inches)
- Materials: Main: 210D high-tenacity recycled nylon; bottom: 420HD Nylon Packcloth
Backpack Storage and Organization
The Mutant 38 has a removable floating top lid with two pockets, both on top. The zippered bottom pocket is the larger of the two and is sized for gloves, hats, food, and accessory items. It also comes with a key fob. There’s a smaller pocket on top of that which is large enough to hold a Smartphone, a GPS, or a satellite messaging device like an inReach or a Spot.
If you want, you can take the top lid pocket off the pack to save weight and cover the drawstring closure at the top of the main compartment with a speed lid which is permanently attached underneath it. While this eliminates the top pockets, Osprey has thoughtfully inserted a third mesh pocket at the top of the main compartment where you can carry small essentials. It’s not large enough to hold a ski mask, but there’s plenty of room for electronics and personal effects.
The main compartment has a hydration pocket with a central port and a hang loop to suspend a reservoir. Otherwise, the space is wide open for stuffing layers and other soft gear. Since this is a winter pack, there is less of a need to line the inside with a plastic bag as long as you remain in freezing temperatures and pack your gear in water-resistant stuff sacks.
Compression and External Attachment Points
The Mutant 38 is loaded with external attachment points to carry bulky or pointy winter sports gear that can’t be stored inside the backpack.
- There are two tiers of compression straps along the sides that are long enough to lash snowshoes to the sides of the pack. Both compression straps are secured with glove-friendly side-release buckles, which makes it easy to attach gear and remove gear in the cold.
- The pack comes equipped with two universal ice axe holders and elastic shaft holders.
- There’s a webbing strap that runs over the top of the main compartment and can be used as a rope carry, together with the floating lid and side compression straps.
- Daisy chains run down the front of the pack along with two additional webbing straps that can span them or can be moved elsewhere. It’s easy to clip microspikes to the daisy chains or you can secure crampons or a crampon bag with the webbing straps.
- There is a 3-point haul system for pulling the pack up a cliff when climbing.
- Reinforced side straps enable an A-frame ski carry.
Backpack Frame and Suspension
The Mutant 38 is an internal frame pack with two aluminum stays and a stiff plastic framesheet. They’re tucked into a sleeve behind the interior hydration pocket and removable if you want to save weight. The back panel below the shoulder straps is tapered narrowing to 8″ wide at the waist end and widening behind the shoulders. The narrow width provides more arm clearance if you use the pack with trekking or ski poles.
The back panel is covered with a snow-shedding fabric that sits close to your back for optimal load transfer. Previous versions of the Mutant also came with a bivy pad to pad out the frame sheet. That bivy pad is no longer there in this version of the pack. As a result, the pack can become quite warm if you carry hot water in Nalgene bottles in the main compartment and that warmth can make you sweat quite significantly.
I found the best remedy is to insert segments of a foam sleeping pad like a Zlite behind the frame to provide more insulation so you sweat less. I always carry a cut-down Zlite in my pack in winter so I have some ground insulation in case I’m injured and need to spend an unexpected night out. Another tactic is to position your hot water bottles as far away from the back panel as possible so they radiate less heat through it. This is really the only thing I found problematic with the Mutant 38.
The hipbelt wings are sewn directly to the back of the pack and come with gear loops instead of pockets, so you can rack gear climbing or snack bottles onto them with carabiners. The hipbelt closes with beefy push-forward webbing straps for mechanical advantage (useful when wearing winter layers) and the hipbelt closes with a beefy, glove-friendly buckle that won’t get jammed up with snow like a smaller minimalist buckle.
The shoulder straps have load lifters, hydration loops, daisy chains, and an easy-to-adjust sternum strap. Both the shoulder straps and hip belt are lightly padded and covered with the same snow-shedding fabric as the back panel. I don’t mind the light padding on this hipbelt because it sits on my iliac crest (hip bones) perfectly and doesn’t slip.
I will be the first to admit that I have a fetish for alpine-style backpacks, mainly because I like to strap all kinds of bulky gear to the outside of my backpack when winter hiking and mountaineering. This new version of the Mutant 38 scratches that itch like never before. It’s a fun pack to carry and a veritable swiss army knife when it comes to the ways you can use it. Highly recommended!
If you need a higher volume version of the Mutant 38 for winter overnights, check out the new Osprey Mutant 52, which builds on the same feature set
Disclosure: The author owns this backpack.SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.
Looks like an excellent pack for alpine sports.
I own an Osprey EXOS and love it. Their designs are well thought out and tested.
Excellent review of a great pack. I also use it for winter day hikes and love its flexibility and comfort. I’ve had mine for several years and it’s held up very well. The 38L capacity seems to carry all my winter essentials, even on solo day hikes. Not large enough for overnights, but it’s not advertised as such.
Len – I suspect you have a different model since this one just came out.
Yes, I’m sure I do, but it sounds like they’re pretty similar in many ways.
Have this in the REI cart right now, wondering though is there a specific one for women before I buy?
I used to read this site a lot when i was first getting into backpacking in ~2014. Have the reviews always been this… rote? it would be better with more critical evaluation of the product, you know, actual reviewing, rather than just summarizing the manufacturer’s feature list. this read’s like Osprey’s page on the mutant 38. how many days did you test it? what were the conditions? You mention ski carry, hauling… did you test any of these features? Why should I care about them? You neglect to mention the nanofly and robic fabrics which are the main change in this version of the pack. Robic is legendary for its durability in ULA packs, something I noticed firsthand when I thru-hiked the PCT. Anyway, just saying this review could be more thorough instead of being a rehash of the Osprey talking points.
I really object to your assertion that I’ve reiterated Osprey’s talking point in this review. This review was based on using the Mutant for about 2 months in winter (~25 high peak summits) in the White Mountains of New Hampshire and many observations about what you can and cannot do with this pack are baked throughout this review. I haven’t changed the way I review backpacks or any other gear in the past 13 years (ie. we actually use them). It’s not that I’m not open to criticism, but I don’t feel bound to the conventions of other gear reviewers.
You do realize that Nanofly and Robic are just hyped nylon, right? There’s really isn’t anything all that special about them despite how much the gear manufacturers want you to believe it adds significant value. It’s marketing. ULA packs are only tough because they use 400D Robic. That’s really not that magical. 400D anything is bound to be pretty durable.
Philip. I think he’s a spammer. He obviously didn’t read the review. This is your normal in-depth analysis. I bought this pack on your recommendation and I also think it’s exceptional.