Sleeping Bag for All Has 9 Different Sizes: REI Magma 15 Review

A freezing cold night’s sleep can be one of the worst experiences someone can have camping. You know the one I’m talking about — where you roll over to a different side every hour, contemplating when the dang sun will come up so this terrible night’s sleep can be over.

That’s what first crossed my mind when REI told me it was ditching the gendered sizes in its Magma line of backpacking sleeping bags in favor of universal sizing and construction.

Because I once worked for a major outdoor brand on the product team — working on sleeping bags, tents, and backpacks — I had serious doubts about REI’s move. I know men’s and women’s sleeping bags are not created the same way. For a women’s sleeping bag to reach the same temperature rating as a men’s, it needs roughly 10-20% more insulation. So the new Magma sleeping bags eschewing gendered temperature ratings set off some alarms for me.

In short: The Magma sleeping bag is one of the bestselling backpacking bags on the market, so this marks a big leap for REI. For testing, GearJunkie received two sleeping bags, one for a male and another for a female to try out. Together, we tested fit and function of the Magma 15-degree sleeping bag. The 2024 Magma sleeping bag performs very well for an 850-fill-down mummy bag, and the wide range of sizes ensures the majority of shoppers will get a bag that fits them. There are a few cons, though.

Shopping for a bag? Check out our guide to the best Backpacking Sleeping Bags of 2024.

REI Magma 15 Unisex Sleeping Bag Review

No Genders, More Sizes

Traditional sleeping bags typically have two to three sizes. For men, regular and long, sometimes extra long. And for women, short, regular, and long. And sometimes, brands include a “left-handed” variant.

In an effort to accommodate an even wider array of users, REI introduced not just three or four — but nine sizes for the redesigned Magma sleeping bag. Sizing options for Magma are Short-Narrow, Short, Short-Wide, Medium-Narrow, Medium, Medium-Wide, Long-Narrow, Long, and Long-Wide.

Part of the reason REI shifted from gendered sizing to a wider array of size options owes to the sleeping bag’s function. The insulation in a sleeping bag works most effectively when there are fewer air gaps for heat to escape.

If a sleeping bag (or down jacket) fits you well, it will prevent your body heat from escaping. Some heat will escape naturally because insulation and the fabrics are air-permeable. If you were to design a sleeping bag made with non-air-permeable fabric, it would be very warm — and way too sweaty.

The Magma offers both 15– and 30-degree temperature ratings, has a mummy shape, scuba hood that cinches, a single-side anti-snag zipper, vaulted foot box, and a draft tube and collar — all the makings of a well-designed, three-season backpacking sleeping bag. The biggest differences between the previous iteration and this one is the design and sizes, and the lack of a 10-degree rating option.

It’s designed to be very lightweight and compressible, with 850-fill, Bluesign-approved water-resistant goose down. Like the previous version, the zipper slides well, and the hood and draft collar are excellent for warmth.

Male Testing: First Impressions

I tested the Long bag (medium-width), while my co-tester, GearJunkie editor Mary Murphy, tried out the Medium bag (also medium-width). Aside from the sizes and genderless design, the Magma Sleeping bag closely resembles the previous iteration.

I camped in the windy desert outside of Cañon City, Colo., for a weekend of climbing at Shelf Road. As those who have camped in the desert know, cold temps come on fast. After a balmy day of climbing in sunny, 60-degree conditions, the temperature started to plummet right after sunset. The first night I tested the bag, the temperature hit the mid-30s.

My first impression of the Magma was how well it fit (read: how tight it felt). This is probably because I spend most of my time in a wide bag designed for car camping. However, I imagine most people will share a similar first impression of the Magma — it is a mummy bag, after all.

After I channeled my inner Brendan Fraser and took on The Mummy (tip your servers), I found the bag comfortable and warm. If anything, I was too warm in the bag. But I run hot, and like my sleeping conditions to be on the cold side.

All in, the sleeping bag performed as expected. It kept me warm and fit me well without having any pressure points or areas where my body was pushing too hard up against the insulation. On the whole, I slept fairly well.

In terms of fit in my Long bag, it was snug, but I could still wiggle my arms and legs around a little bit. Remember, this is a bag meant for backpacking, and it shaves weight where it can. It fit like many mummy bags I’ve tried in the past.

There was plenty of room in the feet, and REI really packed insulation into the footbox. In my testing, my feet were probably the warmest part of my body through the night (I even went sockless).

But the real test of REI’s sizing and gender-neutral overhaul is how well it suits both men and women. Enter our second tester, Mary Murphy.

Female Testing: Magma 15 Impressions

At 5’8″, I am taller than the average woman. But I am also very skinny. My measurements for testing fell squarely in the medium-height range of 5’5″ to 5’11”. And in terms of narrow, medium, or wide width, my hips measure 39 inches. This put me on the cusp of two size options — but the medium bag felt better once I was inside.

The medium bag proved great in terms of fit and length, and fairly good in terms of width. I had enough room in the hips and shoulder areas, and it didn’t feel overly narrow. I also recently switched to side sleeping. For that reason, I opted for the medium-width bag, and though I did side-sleep in the bag for one night, it wasn’t the most comfortable.

Compared to other mummy bags I’ve owned, the Magma was still snug and lends itself better to back sleepers. So, I would not have wanted a narrower size.

I tested this bag on a long weekend getaway in southern Colorado, a hut trip, and a few winter ice climbing trips (an opportunity to push the temperature rating), and paired it with two different sleeping pads to further test it as a system.

I was happy to discover the warmth of this 850-fill bag was comparable to, if not better than, other bags of the same rating. My body tends to run warm, but I also don’t have a ton of body fat, so being cold backpacking is sometimes an issue. Compared to gendered women’s bags that typically have more insulation, I couldn’t tell the difference.

Prior complaints from past Magma owners and testers were that the 15-degree bag didn’t quite perform down to its ISO temperature rating. I tested my bag (alongside a 5.1 R-value sleeping pad) down to 15 degrees during my hut trip, and found it plenty warm. After testing, I’d say Magma’s advertised comfort rating of 21 degrees F is spot on. (I didn’t test it to its ISO lower limit, which for the new Magma 15 is 9 degree F.)

As a lefty, I appreciated the ease of use of both the zipper and the hood’s cinch cord. Also, the “worm-like” draft tube may look odd and flop around, but it did a great job at blocking wind and cold.

Finally, the Magma’s footbox, though very well insulated, is a bit bulky. Even for a mummy bag, it felt narrow. Happily, my feet were never cold, even when I tested this bag down to 15 degrees (just below the comfort rating).

Will This Bag Fit Me?

Because there aren’t genders associated with the Magma sleeping bag, some customers may be a little confused at first. Both our testers agreed on this: the sheer number of sizes is great, once you learn to decipher them. The last thing someone wants is a bag that is too tight or too loose, or not warm enough.

Each REI store is slightly different, but Denver’s flagship location has a dedicated area to lie in a sleeping bag. As part of this test, Nate went through a typical in-store fitting with a sales specialist. This allows customers to try zipping the bag up, wiggling around, and practice rolling over.

REI has offered this “try it out” service for years, but it’s perhaps never been as important, given the range of sizes the Magma now offers.

Drawbacks

The key drawback to the Magma bags is the stuffsack. An 850-fill-down sleeping bag should do an excellent job compressing down to nearly nothing. But the stuffsack REI ships with the Magma bag doesn’t have any compression straps.

If packability is a major necessity for you, you’ll be best off purchasing an additional compression bag to accompany this bag for backpacking trips. This is fairly annoying especially considering how well it can compress, and considering the $429 purchase price.

But this is a minor complaint to a high-performing sleeping bag that pushes the industry’s sizing conventions.

The only other drawback, ironically, is related to fit. Specifically, the shape of the bags. Because these bags work off the same silhouette, they may not fit every body or shape perfectly.

Typically, if a brand manufactures a sleeping bag that will get ISO tested, it will design the shape of the bag according to men’s and women’s conventional physiques. Men’s bags will have wider shoulders and be taller. Women’s bags will have wider hips and narrower shoulders.

So, a concern of ours was that REI’s Magma could be ill-fitting in the hips or shoulders depending on one’s body type, because of the unisex fit. While both testers found the fit acceptable in this review, both agreed their bags fell a little on the snug side.

We asked REI about this, but the brand did not find this point too concerning.

“While it is true that women’s shoulder measurements are in general narrower than men’s, [there isn’t] significant overlap between women’s and men’s when looking at body scan data,” REI told GearJunkie. “The size of a sleeping bag is not synonymous with fit of a sleeping bag.”

And this underscores the importance of finding the ideal size for your body. We only sampled two sizes, you will want to experience the feel of the Magma firsthand by trying on one of the bags yourself in the store.

REI Magma 15 Sleeping Bag: Final Thoughts

GearJunkie had two people (male and female) and two sizes in testing, though looking at the range of sizes offered, this is still limited feedback. In our brief testing of the bag, the Magma performed really well. Its impressive low weight, 850-fill warmth, and price point make it a contender for one of the best bags for backpacking.

All in all, there was enough insulation for both our male tester and our female tester to get a good sleep between the 15-degree and 21-degree comfort rating (and above toward the 30-degree mark).

But the key to this piece of gear lies in the fit. While maybe a tad snug in the medium-width options, overall the fit was better than other “standard” bags.

If you’re considering purchasing a Magma sleeping bag, go to an REI store to find which of the nine sizes best fits you.