Osprey Mutant 38

9.0 score
[Editors rating (9.0) + Users rating (10.0)] / 2 = (Gearweare.net) score (9.0)/10

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Editor rating: 9.0 / 10
User's rating: based on 1 user ratings
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Osprey Mutant 38 Review Facts

Osprey’s Mutant 38 is a functional, durable, and lightweight addition to their Mutant series of climbing backpacks. With over 40 years of business under their belt, Osprey certainly knows what customers need for a day trip in the mountains. They have designed the Mutant 38 with short excursions in mind, as its mid-range size is perfect for a quick and easy ascent. With all of the essentials and none of the frill, this bag is built for comfort and ease, without compromising its strength.

Editor's Pros & Cons
  • Comfortable, durable, and lightweight design
  • Specialized for alpine climbing and cold weather
  • Holds a surprisingly large amount of gear for a slim bag
  • Lifetime guarantee
  • Minimal amount of pockets
  • No attachments designed specifically for crampons
  • Waist belt is not a universal fit
  • May not hold enough weight for longer excursions


The Mutant 38, named for the volume of liters it can hold, is the middle child in the Mutant family. It is a nice mid-size option compared to the hefty Mutant 52 and the mini Mutant 22. There are options to purchase the small/medium version, which holds 36 liters, or the medium/large version, which holds 38 liters. If you think of space in terms of items rather than volume, it is possible to a light sleeping bag and pad, rope, tools, food, and water for a few days, winter clothing, and more. At this size, the Mutant 38 provides enough room for essential climbing gear without weighing you down.


This pack weighs in at under 3 pounds – the small/medium is 2.67 pounds and the medium/large is 2.81 pounds. Despite a sleek design and smaller volume (compared to packs designed for longer trips), the Mutant 38 can still hold up to 50 pounds to accommodate almost any gear that you may need. And while it was created for quick winter trips, this mid-range pack also works well for longer trips in warmer weather. Whether you are on a day trip in the mountains or on a long weekend hike, this backpack is a perfect size.


Although the Mutant 38 is designed to be secure and comfortable for most users, some owners of this pack have noted that the hip belt is not the perfect fit for everyone, so it is important to make sure that the small/medium waist fit of 26”-45” or the medium/large fit of 28”-50” will meet your personal needs. The small/medium fits torso lengths of 15”-19” and the medium/large fits torso lengths of 18”-22".


The Mutant 38 is designed to be durable, flexible, and resistant to water and snow. It is constructed with a sturdy 210D high tenacity nylon with honeycomb accents, and the bottom is an even sturdier 420D packcloth nylon.

The snowshed fabric back panel has (removable) internal aluminum stays that are flexible enough for easy maneuvering, but sturdy enough to keep the pack’s shape. The laminated, padded shoulder straps and contoured foam hip belt are built to keep you comfortable and dry. The sternum strap even has a built-in safety whistle so you always have one on you in case of an emergency.


Although the Mutant 38 is already lightweight, it also offers options to adjust or remove features that you may not need on a certain climb. If you are using a harness, the hip belt can be tucked away behind the pack. The HDPE frame sheet and the dual stays in the suspension can be taken out, and the side compression straps are completely removable.

The entire top lid (brain) can also be taken off, but the built-in “FlapJacket” – which is like a poncho that covers the top of your bag – allows you to do this without compromising water and weather protection for the gear inside. This feature has been touted as a personal favorite for many Mutant owners, as it removes unnecessary bulk and weight and still provides easy access to the main compartment of the bag. These optional tweaks allow users to customize the pack for their needs, making it a versatile addition to your outdoor gear that can be used year round.

Pockets and Attachments

The Mutant 38 is designed to be a streamlined pack for short trips in the mountains, but it still has a number of clever features to help tote your essentials. Helmets can be carried in the top pocket, which has a removable mesh attachment designed for this purpose, (or they can be attached to the front of the pack as well). The top lid design fully protects your helmet without getting in the way. The top lid also has a separate pocket for rope and other gear – or snacks!

The Dual ToolLocks on the bottom of the pack has bungee tie-offs that will safely and securely hold your ice tools. The pack has gear loops and attachment points on the hip belt, which many owners have raved about for its smart design and necessary convenience. There are also webbing loops on the front panel for attaching crampons or other additional tools you may need for your particular adventure.

Despite boasting its simplicity, the Mutant 38 even has A-frame ski loops so you can easily attach your skis and enjoy a smooth ride back down after your climb. Osprey has focused on the necessities with this bag, and even with a few added bonus features the pack does not get bogged down with too many pockets and straps.


One of the best features of this backpack is a small, but brilliant detail – glove-friendly buckles and zipper pull. If you have ever been in a situation where you are out in the cold and need to quickly grab something from your pack, you’ll understand just how important this is.

If you need to take the Mutant 38 off of your back during your climb, Osprey has provided a solution with a three-point hauling system which evenly distributes the weight of the pack as you pull it up.


Of course, the smaller size and lighter weight of this pack alone are enough to make it comfortable to use, but its specialized design adds to this comfort for a smooth and safe climb. Its sleek design means that it is not going to get caught or snagged on rocks and plants, which eliminates a problem that you should not have to worry about on your outdoor excursion.

The nylon fabric of the Mutant 38 is both durable and breathable, a best-of-both-worlds combination that is not always found in climbing backpacks. This does not detract from the insulation that the back panel offers, though, so rest assured that this bag holds up in any weather conditions. With comfortable textures, padding, and low-profile straps and belts, this pack will feel like a blessing instead of a burden.


The slim hip belt of the Mutant 38 gives climbers a wider range of motion, which decreases the amount of energy you need to exert – keeping you feeling happier and healthier. And despite being called a “hip belt,” many users will find that the pack sits more on the waist than the hips, which provides even more stability and comfort.

The back panel is sturdy enough to feel supported, but the flexible and adjustable stays provide increased mobility so there is less stress on your spine. At the same time, the pack’s center of gravity is close to your back for security, and its weight is distributed evenly, so there is less strain on the rest of your body as well. (Your shoulders will thank you!) This design is truly focused on reducing fatigue and increasing enjoyment.


Owners of the Mutant 38 have found that the pack holds up under harsh conditions and user wear and tear. Its nylon fabric and well-crafted seams are built for durability and long-lasting use. This does not compromise its simplicity of use or comfort, however – this fabric is still flexible enough for easy packing and movement. And if anything ever does happen to damage the bag, Osprey offers a lifetime guarantee, so you really can’t go wrong with this investment.

Water Resistance

The back panel is built to shed snow so you don’t end up with unnecessary build-up on your back as you climb in wintery alpine conditions. The FlapJacket that covers the pack if you remove the top lid is designed to be “weatherproof,” although some owners have said that “water resistant” is a more accurate description. The main consensus is that as long as you do not drop the pack in a body of water, the gear that you have inside the pack should be just fine.

Hydration Bladder

In the main chamber of the backpack, there is a built-in hydration sleeve which can hold a 3-liter reservoir, but you need to purchase a hydration bladder separately (or, hopefully, use one that you already own). The hose of the bladder can be run through dual ports in the shoulder straps – a handy feature for when your hands are busy doing more important things. Some owners have claimed that the full hydration sleeve is bulky compared to the rest of the streamlined design and that it interferes with the comfortable fit of the backpack. There is plenty of room for water bottles in the main compartment if this becomes an issue for you, but some might say it would be nice to have a pocket designed specifically for water bottles since hydration is vital on any trip, short or long.


The latest version of the Mutant 38 is in a “Blue Fire” color, which is an attractive dark navy blue with hunter orange on the back panel and accents. It also comes in a Black version (my personal favorite), which is all midnight black with a few gorgeous cerulean blue accents. If you prefer something flashier, the early models of the 38 offered a brighter palette with neon yellow on dark olive green.

Comparison to Other Brands

The smooth, light design of the Mutant 38, (and of Osprey bags in general), sets it apart as a quality contender in the realm of climbing backpacks. It has no unnecessary frills, and its simplicity makes for an easier, and safer, outdoor excursion. While many packs have rigid and bulky features, the Mutant 38’s low-profile compression straps, slim hip belt, and flexible back panel make it comfortable and easy to carry, with less strain on your shoulders, hips, and spine. Although this bag might not be large enough or contain enough pockets and attachment options, for a long mountain trip, it is versatile enough to be a smart purchase that can be used in every season.


Since the Mutant 38 is a mid-size and simplified pack, it is designed specifically for day trips in the mountains. It is perfect for beginners and guides on short ice climbing excursions, for hikers and skiers, and even for campers who want a lightweight solution for carrying their supplies. Its rugged capability and surprisingly strong carrying capacity allow it to be used in longer trips as well, especially if you are adventuring in easier conditions that do not require as much gear. On the other hand, seasoned climbers (with excellent packing skills) have used this pack on multi-day trips in wintery conditions with no problems, so this bag can accommodate almost any excursion.

The Bottom Line

Overall, Osprey’s Mutant 38 is a sleek little pack where form meets function. It rethinks what is truly necessary in an alpine backpack and eliminates frivolous additions that just get in the way. Every pocket and strap has a purpose, and the bag is highly customizable. Its comfortable fit gives climbers an increased range of motion and reduces strain on the body, yet it is strong enough to hold up in rough and severe conditions. It holds a surprising amount of gear without being a burden, so it truly excels as a mid-sized backpack that will be a useful addition to any outdoor enthusiast’s collection.