For several years in a row now, the Osprey Mutant is our Editors' Choice Award winner. The Mutant is a feat of pack design and engineering. It has an impressive ability to haul heavy loads with (relative) ease, then mutate into a summit machine. You can strip it down to the essentials for a lightweight summit push while retaining the features you need to keep your technical equipment secure and accessible on the climb. The pack is only 38 liters, but we can pack it with equipment for trips that usually require a 50-liter pack. We attribute this to a thoughtful suite of features and a tapered design that accommodates lightweight but bulky items like jackets or tents at the top of the pack. If your climbing kit is lightweight, we think you'll be able to stretch the boundaries of the Mutant, allowing it to replace at least a couple of packs in your quiver.Check out the bigger cousin to the 38-liter pack in this review, the Mutant 52, an excellent addition to the Mutant series, and one of our favorite packs in the 50-liter range.
Osprey Mutant 38 Review
Compare prices at 3 resellers Pros: Comfortable, affordable, durable, fully featured
Cons: Not as lightweight as some packs
Manufacturer: Osprey Packs
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Our Analysis and Test Results
Hands-On Review of the Mutant 38
The Osprey Mutant is a great pack that gets top marks in all categories, coming out as the Editors' Choice Award for the second year in a row.
The Mutant still doesn't top the charts in our grams per liter measurement, but it still reigns as our Editors' Choice Award winner for the second year in a row due to well-balanced performance across many categories.
This pack offers an average weight-to-volume ratio, which is based entirely upon our in-house measurements of weight and volume. We use an ordinary hanging scale, an out of the ordinary ping pong ball volume test, and a little math. (It's similar to the industry-standard tests, we just use a more readily available ball.) This is our most objective category, and our most important one, weighing in at 30% of the overall score for each pack.
It is important to note that we did not include the lid in the grams per liter calculation. Adding it in creates an unnecessary penalty in a competitive field where many other packs don't feature lids at all. The Mutant has a removable lid and a unique FlapJacket, which can cover the top of the pack even when the lid is left behind. In an inspired design update, the helmet carry flap is now removable as well. So you can still use it on the front of the pack if you leave the lid behind.
Ultimately, a modern pack's weight is all about thoughtful design. A good mountaineering backpack should eliminate redundancies and excess materials, without compromising utility. Osprey designed a brilliant pack in this regard, across all of these categories.
The previous version of this pack carried like a dream. We routinely loaded it up with food and climbing gear for 3-4 day mountaineering trips. We were stunned by its comfort on everything from long trail slogs to steep technical rock and ice climbs.
The previous model featured a single metal stay in the middle of the back panel. For this updated model, Osprey split the stay in half, using two narrower versions on either side of the back panel and angling them in a V shape. We noticed the pack carried differently, but still very comfortably. This shift works with the pack's slimmed down profile to climb even better than before. But it lost the tiniest bit of carrying comfort on the approach.
In the end, it was a wise choice on the part of Osprey. The pack's comfort is now more competitive with our other fast-and-light packs, the Arc'teryx Alpha FL 45 and the Patagonia Ascensionist 40. As climbers, we often accept a little more discomfort on the approach in exchange for excellent performance on the climb.
The other thing we love about this model is that you can remove the framesheet and its stays, but you can leave the foam back panel in place. This lets you slim down for the summit push. We really like having foam in the back panel because climbing gear is often hard, awkwardly shaped, and pokes us in the back if there isn't any structure. The foam can also be removed if you really want to leave it behind or use it as part of your sleeping system. It is a little finicky to put back into place, but totally doable. It doesn't give the pack much structure, however, so we only stripped it down if we were carrying very lightweight and puffy items like jackets — making it great for long ice climbs when the heavy gear is on your harness.
This nudges the pack ahead of the Alpha FL, which has a foam pad sewn in place. All this said, if the pack is part of our sleeping system, we're usually on a big climb and too tired to fiddle with anything mildly inconvenient. So we often just throw the whole pack (contents removed) under our feet.
The shape of the pack is now slimmer and feels more svelte on our backs. The top is wide and often gives the pack a triangular shape. This made it easy to squeeze in those last puffy, soft clothing items in at the top of the pack and helps the whole pack carry nimbly on our hips. We can rotate and move our hips better on the climb and the approach, which is critical for improved hiking mechanics, efficiency, and therefore endurance. This is a pack that you'll love on those 20 hour days in the mountains.
Another key to hip freedom is the narrow hip belt. The padding is adequate and provides enough support for heavier loads, but the narrow webbing keeps the hip belt out of your way when you have a harness on underneath it. This lets it compete with the simple webbing belt design on the Alpha FL. The two take very different approaches but come out with similar climbing comfort and utility.
The narrow, webbing belt on the Alpha makes it less comfortable on the approach, but it stays well out of the way on the climb, and you just use the gear loops on your harness. The Mutant has useful gear loops on the padded portion of the hip belt, which blocks your rear gear loops, but the thinner webbing up front allows improved climbing movement and access to your front gear loops. Both packs offer similar performance with very different styles.
The Mutant revolutionized our expectations for climbing pack comfort. Our physical therapist helped explain exactly what is 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 with 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 better than any other climbing pack we have tried.
For a complete discussion on carrying comfort, check out our buying advice article, complete with advice from a long time mountaineer and physical therapist in the Pacific Northwest.
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. The Osprey excels in this realm as well with highly breathable materials and a ribbed texture in the foam back panel. 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.
Last, the shoulder straps on the Mutant are a firm but thin foam. Some may question the comfort, but we swear by it. The firmness ensures improved movement, and the pack stays with you for those technical moves. It also effectively distributes the load over the width of the strap. Fluffy, soft padding just gets compressed under heavy loads and only feels comfortable when you try it on in the store. With a few changes to this year's model, we still rate the Mutant 38 at the top of the Comfort metric.
Lightweight fabrics are not known to be durable. Typically, there is a tradeoff between lighter weight and durability. As climbers, we weigh our priorities (pun intended) for one over the other.
Osprey uses 210 denier nylon for most of the pack, a very common linear mass density of fibers used in mountaineering packs. In contrast, expedition packs like the Black Diamond Mission 75 and special-use packs like the Mountain Hardwear Scrambler (a rugged rock climbing backpack) use 420 denier fabric. With this update, Osprey added 420 denier nylon packcloth to the bottom to help the pack stand up to repeated drops on rocks, improving its durability.
The only pack that beat the Mutant in the Durability metric was the Mountain Hardwear Scrambler due to its rugged materials, and simple, durable design. Several of these packs feature more durable fabrics, but this doesn't tell the whole story when we use the packs in the field. The Mutant still scores ahead of most for strength where it is needed and well-made features that don't fail or wear out with use.
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 find 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!
In our first year reviewing the Mutant, it blew us away — this time metaphorically and without straps flogging us in the face, which was awesome. We overloaded the pack with 4-5 days worth of alpine climbing gear and food (and we eat really, really well when we're in the mountains). The pack carries impressively well, even when crammed with 50 pounds of gear for the approach to our alpine basecamps, making it a very versatile pack.
The closest competition for the Mutant in the Versatility metric is the Patagonia Ascensionist. This is a very similar pack in many ways, with just a little less versatility. The Mutant has a proper (removable) lid if you want it, and the stowable FlapJacket covers the opening if you do leave the lid behind.
Osprey also made the helmet carry removable instead of sewn into the lid so you can carry your helmet on the front of the pack when you're leaving the lid behind. (It clips easily onto the front daisy chain loops.)
For some of our testers, this pack still had an excess of features for their climbing taste. The Alpha FL, our other favorite pack (and award winner), swings the pendulum in the opposite direction. It has no side straps and a simple elastic cord braided on the front to hold crampons or other overflow items.
Osprey also did away with the complicated quadruple side strap design and went to a traditional dual design, with only the top strap using a buckle that comes completely undone. This is a tried-and-true design, highly functional for climbing uses. The lower strap can only be loosened, and it is just big enough to tuck a 3/4 length foam pad into it.
Osprey now also makes two more sizes of Mutant packs, a 22 liter and a 52 liter size. We tested the Osprey Mutant 52 as well, and while it is not quite as versatile as the 38, it is an excellent addition to the series for those who prefer longer, bigger, or more complex objectives and need just a little more pack capacity.
Osprey further refined the features on this year's updated Mutant, and, overall, we really appreciate the changes. There were two, however, that we were not thrilled with — The loss of the internal mesh pocket and the new front attachment point for the rope attachment strap.
We appreciate the irony of our previous criticism of Osprey packs for having too many features and our complaint that they eliminated a pocket. But that internal mesh zippered pocket was great for the days you left the top lid behind. Now, it is easier to lose small items like chapstick, headlamps, and snacks when you ditch the lid.
The rope carrying strap is an excellent addition, but they anchored it to the front of the pack, and if we don't clip it in, it just dangles on the outside of the pack and gets in the way of our ice tools, crampons, etc. This is a flashback to our objections to Osprey packs with their history of strappy, flappy designs.
Another minor flaw is that the points where you secure the shaft of your ice axe or tools overlap with the buckles that close the pack, which is often inconvenient.
There are other updates, however, that we really like. One is the switch to the simple dual side strap design (instead of the complicated z strap system with four side straps to contend with). This is tried and true in climbing packs, and we dig it.
And we love that removable FlapJacket cover and helmet carry pocket. You can now carry a helmet on top of the lid, which we love for ergonomics and helmet protection (so you don't crack it when you set your pack down), or on the front of the pack. We don't like the front-carry as much due to the possibility of setting your pack down on the helmet and damaging it. It also adds weight to the outside of the pack, pulling the center of gravity away from your back (unless you have an ultralight helmet, which we recommend). However, this does allow an external helmet carry if you want to leave the lid behind. Excellent attention to detail.
Overall, the fleet of features on this pack are still excellent and highly practical for the technical alpinist or general mountaineer.
The hip belt design is fantastic. 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. It's also improved performance and comfort when wearing a harness. The gear loops are convenient, as is the ice clipper attachment sleeve. The hip belt design is a very smart blend of features for excellent support on long approaches with heavy loads, minimal interference with your climbing movement on technical pitches, and easy access to your gear on the climb.
And while there is no formal crampon attachment, those same daisy chain loops designed to allow a front helmet carry also provided anchor points for a trusty ski strap. We often threaded a ski strap and attached our crampons to the front of the pack. Otherwise, you can put them carefully inside the pack.
Brilliant. Thank you, Osprey. This pack is still a game changer.
The Mutant is a beast on long, grueling approaches, and nimble on technical climbs. It is one of the most well-balanced alpine climbing packs we have ever used. This pack manages 50-pound loads, expanding to fit gear and food with the ease and grace of a pack at least ten liters bigger.
We love this pack for climbing in the Pacific Northwest, where approaches can be long and arduous, and then you want to shift gears and have an excellent, lightweight climbing pack for a technical ice or alpine objective. This pack strips down to a nimble and lightweight summit pack, complete with features to facilitate steep, technical climbing. This pack was so versatile and durable that it became our go-to for everything from ski mountaineering, fast-and-light alpine climbs, long mountaineering objectives, and even mellow days at the crag.
If you want just a little more volume, the Mutant 52 is an excellent, and logical, choice.
The Mutant is priced more like a 30-something liter pack at $170, but in our field tests, we found it useful on trips we would typically think to bring a 50-liter pack. This expands the utility of the Mutant from days at the crag to 4-5 day mountaineering trips, greatly reducing our quiver of climbing packs. With limited storage space, we're psyched on that.
The Mutant has been popular among many of our colleagues. As professional mountain guides, we use, and abuse, a whole lot of gear. Several guides have kept their Mutant packs through multiple seasons, an impressive feat for the number of days we spend in the field. During our first round of testing, we climbed with now-IFMGA Certified Guide Karen Bockel, who was training for her last exam. She was climbing with the Mutant and loved it. We climbed the North Ridge of Mt. Baker in a day at the end of the summer—in icy and challenging conditions. Bockel mock guided two of us up 7,000 feet, much of it on technical, late-season glaciated terrain. We carefully observed all of her systems, from rope techniques to the gear she chose. It was an inspiring and athletic ascent. The Mutant was up to the task.Now in our third year of testing the Mutant, we are pleased to report that the ongoing updates have indeed improved the quality and performance of the Mutant, and it remains our Editors' Choice Award winner.
— Lyra Pierotti