The Osprey Mutant 52 is a dream come true for our alpine-centric testers. When we first tested the Mutant 38, we were stunned. It was far and away the most comfortable and versatile mountaineering backpack we had ever tested It is fully featured enough for any mountain pursuit, and light enough for our fast-and-light day missions. Further, there was something about the suspension design that really made it climb impeccably well. We dreamed of another version with a little more volume to make some of our longer, multi-day climbs and winter endeavors more accessible—we were straining the poor little 38-liter pack so much it should have burst at the seams.Osprey answered our dreams when they released the 52-liter version. The bigger size does mean it is less optimized for steep, technical terrain, but we love it for longer trips, winter climbs, overnight ski tours, and more complicated objectives. This is an excellent pack for use on long alpine routes, where the terrain may be moderate but sustained, so a svelte and comfortable pack that climbs relatively well is key.
Osprey Mutant 52L Review
Compare prices at 2 resellers Pros: Durable, versatile, fully featured for all mountain pursuits
Cons: Closure system limits ability to overstuff, larger size less ideal for more technical routes
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Our Analysis and Test Results
The Osprey Mutant 52 is an excellent all-around mountaineering pack for longer trips, more complex objectives, and multi-day adventure in winter conditions.
The Mutant 52 does not hold quite the same standard in this metric as its smaller cousin, the 38-liter version. We think the main reason it falls behind in this category is due to the collar design of the main compartment. This pack has an asymmetrical collar which does not extend upward in a cylindrical fashion like most similar mountaineering packs. This makes the opening very wide, and makes packing easier, but it reduces the amount you can cram into the top of the backpack. With a more cylindrical collar, we can stuff a lot of compressible items, into every inch of the expandable space. Then we could compress it all down with a center strap or the lid of the pack.
Otherwise, the material and ease of packing remains similar to the Mutant 38, with slightly stretchy fabrics that allow you to squeeze something in to every last inch of this pack—up until you run out of room at the collar. To keep this pack reasonably comfortable, we think it was a wise choice to limit the size of this pack, and make it difficult to truly overstuff it.
Osprey advertises this pack at 52 liters, but in our ping-pong ball volume test, we measured 47 liters. The 38-liter Mutant measured 37 liters in our test. Subjectively, we also felt that the 52-liter Mutant did not carry quite as much stuff as other 50 liter packs. When we review the results of our Volume Test, it made sense to us that another popular pack in this range, the Black Diamond Speed 50, actually measured in at 52 liters.
As climbers, we are always trying to carry the smallest pack possible, to improve comfort on the technical part of our climb—at a slight cost to comfort on the approach. Osprey keeps us honest with the Mutant 52 by truly limiting how much we can overstuff this pack, forcing us to be thoughtful about what we bring. And realistically, with good strategy and a little thought, this pack works out very well for multi-day mountaineering objectives.
Since we tested the Mutant 38, we have been dreaming about a pack of every size made in its shadow. Osprey answered our dreams with the 52, one of the most useful and versatile pack sizes for mountaineering.
We had already been pushing the limits of our 38, loading it down for up to 5 days worth of food and gear for summer mountaineering trips. With the 52, this was a much more reasonable endeavor, and we could fit more items inside the pack instead of looking like a walking yard sale.
The back panel has a removable plastic sheet with two metal stays. This sheet provides excellent support for heavier loads and is very easy to remove when you get to basecamp and gear up for a technical climb or ski descent. There is also a removable foam sheet in the back panel. If you leave this in place, it makes for an excellent, comfortable summit pack. It is just thick enough to provide a smooth, yet supple surface that contours to your back, making it feel secure, ensuring the pack moves well with you on the technical portion of your climb or descent. When the pack is full with your equipment for basecamp, we recommend keeping that plastic sheet in place so you don't end up with a fuel canister pushing awkwardly on your back.
Admittedly, for many objectives, we still choose to cram our 38 to the max to have the climbing comfort of the smaller bag on the technical portion of a multi-day climbing trip. The comfort and more compact size is outstanding. However, the 52 fills a very important niche. For winter mountaineering or multi-day ski touring, trips where you need a bigger sleeping bag and more puffy layers, this larger version provides very impressive comfort on the approach, a secure fit for skiing, and excellent ease of movement on climbs. This is an impressively comfortable backpack for the 50-liter size range, only moderately less comfortable than its smaller counterpart.
The 52-liter Mutant is nearly identical to the 38-liter version: same colors, similar features, and roughly the same materials. This pack also features mostly 210 denier high tenacity nylon. This fabric is a good compromise between lightweight and durability.
In our extensive field testing, we had no durability issues whatsoever with this pack—no holes or signs of abrasion on the fabric, and no bursting seams or manufacturing failures. We loaded this pack down and stuffed it to the brim, and this Mutant adapted to it all.
The Mutant 52 is not quite as versatile as its smaller cousin, the 38-liter—but is still highly versatile. Due to the larger size, this pack will cover a broader range of activities that require more gear or more days than the 38 could manage. The 38 and 52-liter versions overlap in the 3-5 day summer mountaineering objectives. The 52-liter backpack will certainly work for fast-and-light summer climbs, but it will feel a bit bulky and cumbersome. That said, if you're looking for a true quiver-of-one mountaineering backpack, this is a solid candidate.
The Mutant series is aptly named—it can change and adapt to a variety of conditions and applications. The 52 is a fully-featured mountaineering backpack that is suitable for ski mountaineering, summer and winter mountaineering, ice and alpine climbing—just about anything the mountains might require.
From top to bottom: we love the helmet carry on top of the lid of the backpack—this reduces the risk of dropping your heavy pack on your helmet (many helmet carries put the helmet on the front of the pack). We love the removable lid and the flap underneath that covers the opening of the pack when you remove the lid. Sometimes we would mix up the buckles for the flap with the buckles for the lid, so some color coding would be nice there.
Many lightweight packs eliminate features to keep them light—the Mutant series remains impressively lightweight without eliminating any features. This is most notable with the side straps—this is a great pack for ski mountaineering, as you can easily slide your skis through the burly side straps and carry them in an A frame.
The pack also has one of our favorite ice axe/ice tool attachment systems. It has T bars with elastic that thread through the head of your axe or tool and a simple sleeve to tuck the pick into and secure it in place. Some packs use a buckle around the head of the axe, but for technical tools, this sometimes doesn't work—the head can be too small that it slides out of the strap.
There is a daisy chain of thin webbing sewn to the front of the backpack which perfectly fits a standard ski strap (which you must purchase separately, and which we highly recommend carrying as an addition to your repair kit anyway), and allows you to strap crampons to the front of the backpack.
The hip belt has gear loops on each side, making it easier to access your cams and carabiners on technical climbs. The hip belt can make it harder to access gear on your harness, so this is a nice feature to keep your gear close at hand.
The Mutant series of mountaineering backpacks overlap perfectly to cover all your climbing needs. The lighter versions (22 and 38 liters) are excellent for rock climbs and alpine climbs up to 3-5 days in length in a summer setting. At the upper end of this range, the 52-liter pack comes in to play. This is an excellent pack for longer trips, higher altitudes, extended ski tours, complex objectives, and colder weather climbs. It will certainly work for shorter and faster-and-light objectives, though it may feel cumbersome or bulky when you strip it down for the summit push.
At $200, the Osprey Mutant 52 is well priced for its size, and a great value all around. It is the biggest in the Mutant series, and it is less versatile than the 38 liter version for all around alpinism. For slightly longer trips, up to a week for summer trips with an ultralight kit, more gear-intensive trips in the winter, or for more complicated routes involving glacier travel, snow, ice, and rock, this pack will be an ideal companion.
The Mutant Series is our favorite fleet of fully-featured mountaineering backpacks. There are certainly other packs that we prefer for certain types of climbs, but for all-around mountaineering purposes, the Mutants are hard to beat. The 52 is our dream come true for a pack in the 50-liter range, offering more volume without much cost to the carrying comfort. It is not quite as comfortable as its smaller cousin, the 38-liter version, but it is far more comfortable than other 50 liter packs we have tested. Now we are dreaming of a Mutant in the 70 and 100 liter ranges for expedition use!
— Lyra Pierotti