Hands-on Gear Review

Osprey Mutant 38 Review

Editors' Choice Award
Price:  $160 List | $84.50 at Amazon
Compare prices at 2 resellers
Pros:  Comfortable, affordable, durable, fully featured
Cons:  Not as lightweight as some packs, only lid can be removed for summit day
Bottom line:  This is an excellent pack for most mountaineering uses which excels in comfort and versatility, and climbs very well.
Editors' Rating:   
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Measured Volume (liters):  38
Measured Weight (pounds):  2.5
Weight-To-Volume Ratio (grams per liter):  29.87
Manufacturer:   Osprey Packs

Our Verdict

The Osprey Mutant is a groundbreaking alpine climbing pack. This pack hauls heavy loads that larger backpacks can't handle, and then it mutates into a summit machine, climbing technical rock and ice with ease. This was an obvious pick for our Editors' Choice Award, as it excels in all of our testing metrics—and is among the more affordable packs in this review to top it all off. At only 38 liters, we thought this would limit the range of this pack—but we were able to load it up for 4-5 day trips with lightweight summer climbing gear. Osprey nailed it with thoughtful features on the Mutant, making this pack more simple and streamlined than their other packs.


RELATED REVIEW: The 8 Best Mountaineering Backpacks


Our Analysis and Test Results

Review by:
Lyra Pierotti

Last Updated:
Monday
November 20, 2017

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The Osprey Mutant is a brand new thing. It ran away with top marks in all categories, emerging the clear winner of our Editors' Choice Award.

High five  Mt. Shuksan! We loved the Mutant 38!
High five, Mt. Shuksan! We loved the Mutant 38!

Performance Comparison



Weight-To-Volume Ratio


The Mutant didn't top the charts in our grams per liter measurement, but this didn't hold it back at all from winning the Editors' Choice Award.


We awarded this pack a 6 out of 10 in this category, based entirely upon our in-house measurements of weight and volume, using an ordinary hanging scale, an out of the ordinary ping pong ball volume test, and a little math. This is our most objective category, and our most important one, weighing in at 30% of the overall score for each pack.

Our test load for a long weekend on a technical route (assuming your partner is helping carry some items) fit in or on the Mutant  and was still comfortable to carry.
Our test load for a long weekend on a technical route (assuming your partner is helping carry some items) fit in or on the Mutant, and was still comfortable to carry.

This pack ranks fifth out of the eight contenders in this review (for this metric). It is not stellar, but certainly adequate. The other categories more than make up for an average performance in this parameter. We measured this pack at 2.5 pounds. The climbing pack industry is competitive enough that contenders like the Mutant are still plenty light to be a pleasure to use in the mountains. Materials have gotten very light, and engineering very clever. As such, Osprey can include a lot of useful features without accumulating too much extra weight.

Ultimately, a modern pack weight is all about thoughtful design, which eliminates redundancies and excess materials, without compromising utility. Osprey designed a brilliant pack, across all of these categories.

Comfort


The first time we took this pack out, we loaded it with four days of food and climbing gear. It was jam-packed and super heavy—like 50 pounds heavy.


We hiked briskly up 3,000 feet in about 2 miles of trail and another mile off trail through rugged terrain. When we arrived at camp, we dropped the pack to the ground, forgetting just how heavy it was. The pack made a mighty thud, alarming enough that we checked all the seams and bottom fabric for damage, strain, or holes. Nothing. We were impressed not only by its durability but also the fact that we had completely forgotten just how heavy the pack was.

Here the Mutant is loaded up with four days worth of food and gear and we were no worse for the wear after several hours and several thousands of feet of elevation gain. We were pleased and impressed.
Here the Mutant is loaded up with four days worth of food and gear and we were no worse for the wear after several hours and several thousands of feet of elevation gain. We were pleased and impressed.

On the climb to camp, this pack blew our minds. The low profile waist belt allowed much more range of motion compared to any other climbing pack we have used in nearly two decades of climbing. When high stepping onto boulders, moving through scrambling terrain, it felt much less effortful. We realized this was because the pack allowed us to tilt our pelvis upward far more than other competitors, transferring this effort from muscles to simple biomechanics. Since we could move more fluidly over complex terrain, we arrived at camp much fresher and energized.

Still about 4 000ft of climbing left but the Mutant 38 makes it feel easier than a lot of packs  moving with us through a wide variety of terrain types.
Still about 4,000ft of climbing left but the Mutant 38 makes it feel easier than a lot of packs, moving with us through a wide variety of terrain types.

Our physical therapist helped explain exactly what was going on here. Historically, backpacks have had relatively rigid frames and aggressive lumbar support. What climbers have started to learn is that this forces your spine into extension, and pushes your butt out. While this might feel better to someone who rarely carries a backpack, because it puts more strain on your skeleton and less on your muscles, for those who often venture into the mountains, and have a high level of fitness and balanced strength, this restricts motion and ultimately reduces endurance. Climbing packs are increasingly minimalistic, with flatter, softer back panels. Osprey has figured out a way to blend both options with a single metal stay, which we were able to bend naturally into a position of comfort. That said, it was also easy to bend out of place when packed thoughtlessly with rigid items in the wrong spot.

Andra DeVoght  DPT of Insight Physio  examining the Mutant 38. It is quite comfortable  but the frame requires the use of this single metal stays  otherwise  it folds and crumples.
Andra DeVoght, DPT of Insight Physio, examining the Mutant 38. It is quite comfortable, but the frame requires the use of this single metal stays, otherwise, it folds and crumples.

We took notes from other pioneer climbing pack designers and removed the metal stay as an experiment. While this felt great at first, the back panel turned sloppy and slumped down, curving awkwardly outward. It was not necessarily uncomfortable, but it felt strange and did not climb as nimbly as when it fit correctly. We recommend you keep the stay in place but feel free to experiment with the bend to better match your body and facilitate fluid movement.

For us, this typically meant ensuring excellent contact with our back and very slight flexion of the spine. For a complete discussion on this, check out our buying advice article, complete with advice from a long time mountaineer and physical therapist in the Pacific Northwest.

One piece of advice—we often like to sit on our backpacks when taking breaks, but on a couple of occasions, this bent the metal stay. Once we realized this happened, it was easy to bend it back into a comfortable spot, but for at least 90 minutes we were cursing this pack as it stabbed us in the back. Easy fix, it turned out.

Another important aspect of comfort in this category is breathability. We learned this the hard way with a disappointing performance from Hyperlite Mountain Gear. Breathable fabrics are essential for a versatile pack you can use year round. Osprey excelled in this realm as well with highly breathable materials and textures in the back panel and shoulder straps. Some pack manufacturers have tried to resolve this breathability issue by suspending the back panel away from the back and putting a tensioned mesh panel. This puts the load further on your back, however, which compromises comfort and balance for climbing and scrambling. The Mutant keeps the weight close and still manages to wick moisture and keep you cranking uphill.

Phenomenal: 10 out of 10.

Durability


Lightweight fabrics are not known to be durable. Typically, there is a tradeoff between lighter weight and durability, where, as climbers, we weigh our priorities for one over the other.


But Osprey destroys this assumption with its use of slightly stretchy fabrics. We overstuffed this model and then crammed even more stuff into corners, without straining the seams or puncturing the material. It is made of an unusual fabric that bends with every angled object we could throw at it and has the added benefit of making it even easier to pack.

We didnt stress about attaching sharp objects to the Mutant  or scratching around on rock  ice  or in crevasses  for that matter. The materials are smooth  durable  and even a little stretchy in places.
We didnt stress about attaching sharp objects to the Mutant, or scratching around on rock, ice, or in crevasses, for that matter. The materials are smooth, durable, and even a little stretchy in places.

The only contenders that beat the Mutant for durability were our expedition packs (which had better be durable if your life depends upon it for a month or two in the mountains!), and our smallest model, the Mountain Hardwear Scrambler Outdry 30. The Mutant stands alone as a brilliant mix of light weight and versatility, without compromising durability. But if you're looking for the most durable pack for scratching around on in-a-day rock and alpine missions, the Scrambler might be a good match with its exceptionally durable lid materials.

Versatility


First, a disclaimer: many of our reviewers came into this review with a strong bias against Osprey packs for mountaineering and climbing purposes. Typically, we found them to be over-engineered, over-featured, busy, and way too strappy. One of our reviewers sold an old Osprey alpine pack many years ago after getting off a windy alpine climb and having one of the many straps flogging them in the face for hours on end. Enough!


But when we saw this pack, we took pause. Clean, streamlined. We were intrigued. In our numerous field tests and climbs, the Mutant performed beyond our wildest expectations. We routinely packed this pack for 4-5 day trips in the mountains—and yes, we have a well-thought-out, lightweight summer climbing kit, but we also eat really, really well in the mountains, so this often made it heavy and bulky.

And it's a perfect 10, again.

The Mutant is versatile enough to carry skis A-frame. They are easy to mount and remove quickly.
The Mutant is versatile enough to carry skis A-frame. They are easy to mount and remove quickly.

For some of our testers, this pack is still a bit heavy on the features. The Alpha FL, our other favorite (and award winner), swings the pendulum in the opposite direction with no side straps and a simple elastic cord braided on the front.

But back to the Mutant for now. There were a few extra features that at first glance raised the alarms. "Would these be annoying?", we asked ourselves. The first thing we look for in a simple mountaineering pack is whether or not there are redundancies that add complexity or weight to the pack. We saw a couple of things on the Mutant: the top lid closure system and the side straps.

First, the top lids: there is a traditional brain but there is also a flap underneath it, so if you take the brain off, you can still completely close the top of the pack to keep snow or debris out (we wouldn't call it entirely waterproof). This looks like extra and unnecessary fabric—but it turned out to be a feature we loved. Plus, Osprey added an internal mesh zip pocket which made that interior flap more useful even when we kept the brain on. Very thoughtful, overall.

If you remove the brain of the Mutant it has a very secure and weather-resistant flap which clips into place using the same buckles as the brain that you removed. Very efficient and sleek
If you remove the brain of the Mutant it has a very secure and weather-resistant flap which clips into place using the same buckles as the brain that you removed. Very efficient and sleek

Next, the side straps. They weave back and forth four times. Most of our favorite mountaineering packs have two simple straps across the sides. However, when we strapped a picket to one side, snug through all four, and then didn't have to adjust the other side at all to slide a foam pad under only two of the straps, our minds were blown. It was a small learning curve to figure out how to best use these straps, but we ultimately appreciated the modularity and flexibility of the design.

These straps looked busy and complicated at first  but we quickly got used to them and ultimately really appreciated how much flexibility it gave us.
These straps looked busy and complicated at first, but we quickly got used to them and ultimately really appreciated how much flexibility it gave us.

The top buckle, however, has a locking clasp which was by far our least favorite feature on the pack. It creates a two-step process (and is hard to do with gloves on) any time we need to adjust the length of the strap system. But the middle adjustable buckle is a brilliant idea, and since this is a pack many of our reviewers will now be rocking until something better comes along, we will probably just swap out that annoying locking buckle and call it great.

Features


This pack is phenomenally versatile because of the thoughtful features Osprey included—and for the ones it excluded to keep things simple and streamlined.


We ultimately loved being able to remove the brain and still have a proper closure system for the top of the bag, even though it meant extra material. It was small enough that it did not often get in our way when using the brain, and the mesh pocket inside was tremendously useful.

The side straps are an unusual design, but once we got used to it, we loved it (except for that darn locking buckle on the top). We could use all four straps for smaller items like pickets, or just two for bulky options like foam pads Being able to choose two or four straps so easily made packing this model faster than others.

This locking buckle drove us nuts. Ultimately  we just left it unlocked. The locking mechanism is too small to operate easily with gloves on.
This locking buckle drove us nuts. Ultimately, we just left it unlocked. The locking mechanism is too small to operate easily with gloves on.

Overlapping with comfort, we loved the design of the hip belt. It has a small buckle and a very low profile which allows excellent range of motion for our hips—more than we have ever experienced in a mountaineering pack. The gear loop is incredibly handy, and we liked that we could stash it out of the way under a strip of fabric if we weren't using it.

The useful hip belt of the Mutant 38.
The useful hip belt of the Mutant 38.

Another bias of some of our reviewers: many of them don't typically like helmet carrying systems. Usually, pack manufacturers put these on the backs of their packs, so if you hastily drop the pack to the ground, you could damage your helmet (if you have a foam one, especially). That's silly. Plus, it makes it hard to sit on your pack during a break, and we love sitting on our pack (yes, we are hard on our gear).

Osprey nailed this feature, too, and our minds were once again blown. They put the helmet carrying system on top, stashing the mesh stretch compartment into the top of the brain. At first glance, we still thought this was silly; we were sure it would flop around awkwardly and get in our way every time we went to retrieve snacks or water from the pack. Nope. Especially if you have a very lightweight helmet (which we do, and strongly recommend for the reduced strain on your neck—something we didn't think of before using the lightest helmets), this feature stayed out of our way and kept the pack balanced and centered closer to our back when fully packed.

Brilliant. Thank you, Osprey. This pack is a game changer.

Best Applications


The Mutant is one of the best alpine climbing packs we have ever used. It is one of the most versatile packs as well, being lightweight and fully featured. But the biggest thing we appreciated about this pack was how comfortably it climbed and carried abnormally heavy loads. We could pack as much stuff (and weight) into this pack as standard 50-liter packs we use regularly. It became our go-to pack for ski touring, fast and light alpine climbs, cragging, and up to 4-5 day mountaineering trips. With our gear trimmed down to the most minimal and lightweight gear we can afford, this pack was almost always our first choice.

Value


At $160, the Mutant is priced like a 30-something liter pack, but it holds nearly as much as some packs that advertise over 50 liters capacity. It packs very well, and we were able to carry as much as 4-5 days worth of equipment during the summer climbing season. This made this pack useful for a broad range of trips, so if we could only afford one mountaineering pack, this would be our top choice.

Conclusion


A number of our colleagues use this pack, and as professional mountain guides, they use (and abuse) a lot of gear. During the testing period, we had the honor of climbing with guides who were training for their Alpine Guide Exam with the American Mountain Guides Exam (AMGA). We climbed the North Ridge of Mt. Baker in a day at the end of the summer—in very icy and wonderfully challenging conditions. We had stashed bivy gear at the base camp during our ascent so we could stay the night and practice crevasse rescue the next morning before racing back downhill for coffee and pastries at the local bakery. Our lead tester watched Karen Bockel mock guide two of us up 7,000 feet, much of it on technical, late-season glaciated terrain, and observed how dialed and streamlined her systems were. It was an inspiring and athletic ascent.

Karen Bockel belaying reviewer Lyra Pierotti into a crevasse to find a way down Mt. Baker in late season conditions. Karen went on to pass her Alpine Exam and become the 12th woman certified as an IFMGA Mountain Guide by the AMGA. She loved the Mutant 38. We took note.
Karen Bockel belaying reviewer Lyra Pierotti into a crevasse to find a way down Mt. Baker in late season conditions. Karen went on to pass her Alpine Exam and become the 12th woman certified as an IFMGA Mountain Guide by the AMGA. She loved the Mutant 38. We took note.

A couple weeks later, she passed her Alpine exam to become the 12th woman to be certified as a Mountain Guide by the AMGA as an International Federation of Mountain Guides Associations (IFMGA) certified guide. Certainly, the Mutant didn't make that possible, Karen did—with her diligent training, extensive experience, and great attitude. But we took note of every piece of gear she was using. As a true professional, and long time endurance athlete, she knows how to optimize herself and her kit in the mountains. And the Mutant looked to be a good fit. Her only complaint? It's not waterproof. In the Pacific Northwet, sometimes that matters. No, that was not a typo.
Lyra Pierotti

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