This post may contain affiliate links.

REI Flash Air 50 Backpack Review

REI Flash Air 50 Backpack Review

The REI Flash Air 50 Backpack is an ultralight, roll-top backpack that weighs 1 lbs 14 oz. Available in men’s and women’s sizes, it’s quite similar to the REI Flash 55 Backpack (link to our review) with its reconfigurable pack-mod accessory pocket and strap system but is about a pound lighter in weight, has a fixed length torso instead of an adjustable torso length, and does not have a top lid pocket.

Both packs are still available in REI’s online store and while the Flash 55 is about a pound heavier (2 lbs 13 oz), it has better side compression and comes with a roll top closure and a removable top lid which are capabilities that make it more suitable for winter hiking and carrying smaller volume loads in addition to larger ones.

The REI Flash Air 50 is a roll-top backpack without a top lid pocket
The REI Flash Air 50 is a roll-top backpack without a top lid pocket

Like many ultralight backpacks, the Flash Air 50 has a roll-top closure that buckles together on top but not along the sides. It has a large main compartment, open side pockets, and an open front stretch pocket for stuffing layers and looser items you want frequent access to during the day. The Flash Air 50 also has dedicated water bottle pockets, separate from its side pockets, a feature first introduced on REI packs about a decade ago. These are located behind the hip belt and in front of the open side pockets, making it much easier to pull out a bottle while walking. I’m surprised that other backpack companies haven’t mimicked this feature because it makes water bottles so much more accessible and requires very little extra fabric weight to add.

The Flash Air 50 also incorporates the REI Pack Mod system, which lets you customize the pack by adding accessory pockets or straps to the backpack. These include a waterproof shoulder pocket sized for a Smartphone and compression/gear attachment straps (but not the other pack mod accessories available for the Flash 55). You can also add third-party pockets to the pack if you prefer (See 10 Best Backpack Accessory Pockets.)

RELATED: 10 Best Ultralight Backpacks

Specs at a Glance

    • Volume: 50L
    • Weight (total): 1 lbs 14 oz (size medium)
    • Gender: Men’s and Women’s available
    • Frame: Internal, Wishbone-shaped spring steel
    • Torso Length: Fixed
    • Pockets: 8, including Pack Mod mesh shoulder pocket
    • Hydration ready: Yes
    • Load lifters: Yes
    • Seam-sealed: No
    • Torso Sizing: (S: 18 inches), (M: 19 inches), (L: 20 inches)
    • Hip belt Sizing: (S: 32-40 inches), (M: 34-42 inches), (L: 36-46 inches)
    • Maximum recommended load: 40 lbs (our assessment)
    • Materials: UHMWPE ripstop nylon
    • Bear Canister Compatibility: a BV475 fits horizontally at the bottom of the main compartment, while a BV500 fits horizontally but only at the top (extension collar) of the main compartment. The thin cords of the Y-strap fit nicely in the grooves of the BV500 or BV475 canisters and do not bump you in the back of the head when carried on top of the pack (above the rolltop)
    • Optional Add-on Pockets and Straps (available separately) – Waterproof shoulder pocket and extra accessory straps.

Backpack Storage and Organization

The main compartment of the Flash Air 50 is huge and will hold a lot of gear and food: it feels far larger than 50L because REI, like most larger backpack manufacturers, does not count open pockets or the extension collar in its volume computations. It has an internal reservoir hang loop, but the rest of the interior space is unstructured with top access only.  A rain cover is not included with the pack, so you’ll want to line the interior with a pack liner or trash compactor bag, particularly since the thin nylon/polyester exterior fabric does absorb moisture in rain.

There is a Y-shaped cord that provides top compression and can be used to hold a sleeping pad or canister on the top of the pack.
There is a Y-shaped cord that provides top compression and can be used to hold a sleeping pad or canister on the top of the pack.

The sides of the roll-top clip together on top of the pack rather than along the sides, providing less vertical compression.  I prefer packs like those from Hyperlite Mountain Gear that provide both. While the top of the pack bag has a stiffener, it’s quite flexible and only on one side of the roll top making it difficult to get a tight roll unless the pack is stuffed full, and can result in leakage in rain. There is a Y-strap that loops lover the roll top but it uses a long cord not webbing and requires that the pack bag be quite full to provide any compression.

The Flash 50 has a front (solid) stretch pocket bordered on the sides with durable mesh that makes it easy to store damp or frequently accessed items, so you don’t have to stop and open up your pack to access them or put them away. The top of that pocket has a cord lock for added security, but the slack cord hangs free and can get hung up on vegetation if you hike off-trail.

The backpack has two solid sleeves (located directly behind the hip belt pockets but attached to the pack sides) to make it easy to reach the bottles or snacks while you’re wearing the pack. The bottle sleeves are sized for tall skinny SmartWater bottles and it’s easy to pull them out. The sleeves have elastic cords to hold the bottles in place, which is particularly important when you place the pack on the ground and it falls over.

The Flash Air 50 has water bottle sleeves in addition to side pockets
The Flash Air 50 has water bottle sleeves in addition to side pockets

The Flash Air 50 also has side pockets behind the water bottle sleeves for holding gear and longer objects, like tent poles, chair kits, fishing poles, etc, and lashing them to the side of the pack with a compression strap. It’s an important feature, especially on a pack that will be used for long-distance trips. These pockets are not reachable when wearing the pack.

The pack comes with one optional pocket, a mesh pocket that is not waterproof, sized to hold a smartphone. It’s attached to the pack by looping a plastic toggle through a webbing strap on the shoulder strap. Earlier models of the Flash 55 had a waterproof shoulder strap pocket which was much better, but can still be purchased as an add-on. You can also add a third-party pocket, like the Gossamer Gear Shoulder Strap Pocket to the Flash 55 shoulder straps quite easily.

The zippered hip belt pockets are sewn on and not removable. Both are solid-faced and large enough to hold snacks, a Smartphone, or even a pair of fleece gloves

Backpack Compression and External Attachment System

Daisy chains run along both sides of the front stretch pocket and extend up the front seams to the top of the frame. These can be used to lash accessory gear to the front of the pack with carabiners or accessory cords but are somewhat limited because there is only one anchor point along the rear side of the pack alongside the shoulder straps. I’d prefer at least two so you could lash snowshoes or a pad to the side of the pack. While you can get by without this added attachment capability for three-season backpacking, it’s much more important if you plan to use the pack in four-season (winter) conditions when you need to carry very bulky gear on the exterior of the backpack.

Daisy chains along the sides let you attach gear or anchor compression straps
Daisy chains along the sides let you attach gear or anchor compression straps

Out of the box, there is one side compression cord running from a side pocket to a point just below the top of the shoulder strap. One end of this cord runs through a line loc that’s girth hitched to its attachment point, so it’s easily removable, while the other is knotted onto the corner daisy chain. I’ve found such cord-based compression to be virtually worthless for real compression and prefer webbing-based compression straps instead since they’re much wider and will compress gear.

Out of the box, the pack comes with one side compression “cord”.
Out of the box, the pack comes with one side compression “cord”.

The pack also comes with an ice axe loop at the base and an elastic shaft holder attached to one of the daisy chains. It can be used to carry an ice axe or a pair of trekking poles, tips down.

Compression on less than bulging loads is pretty weak.
Compression on less-than-bulging loads is pretty weak.

Backpack Frame and Suspension

The REI Flash Air 50 has a fixed torso length and a narrow size range from 18″-20″ in men’s torsos and 16″-18″ in women’s.  The hipbelt is not removable and is molded into the foam back panel which is covered by fine mesh providing some ventilation between the blocks of foam padding. While not as cool as a suspended mesh back panel, the pack sits very close to your torso and the well-padded and pre-curved hip belt provides outstanding load transfer to the hips, particularly when carrying a heavy or bulky load. I can carry 40 pounds comfortably with the Flash Air 50, which is much more weight than most ultralight backpacks from cottage manufacturers.

The precurved and padded hip belt provides marvelous load transfer to the hips and does not slip.
The pre-curved and padded hip belt provides marvelous load transfer to the hips and does not slip.

The Flash 50’s frame is a lightweight wishbone-shaped steel perimeter wire (not removable). It provides great torsional flex, so it moves with you, as well as the horizontal rigidity that is important for proper load lifter function and hip belt load transfer. The hip belt is sewn directly to the pack so that the load is carried very close to your core muscles and hip girdle for maximum efficiency, while the soft lumbar pad and pre-curved hip belt wings grip the iliac crest. I’m really quite impressed with the hip carry on the Flash Air 50, which is comfortable and does not slip down.

The hip belt closes with push-forward straps for mechanical advantage, with a single central buckle, which I prefer on packs because it can be used while wearing gloves and because it’s better for winter use when snow will clog smaller buckles.

The shoulder straps have multiple attachment points for accessory pockets.
The shoulder straps have multiple attachment points for accessory pockets.

The shoulder straps are S-shaped making them comfortable for men with load lifters. The sterum strap buckle is easy to close and slides vertically making it easy to adjust. There are three horizontal straps on each shoulder pad which are good for use with a hydration system but can also be used to attach accessory pockets.

Comparable Ultralight Backpacks

Make / ModelWeightFabric
Zpacks Arc Haul 60L20.9 oz / 593gUltra 200
Hyperlite Mountain Gear Southwest 5534.9 oz / 989gDyneema DCF
Granite Gear Crown 3 60L32.6 oz / 1040gRobic Nylon
Osprey Exos Pro 5534.6 oz / 981gUHMWPE Nylon Ripstop
ULA Circuit 68L37.3 oz / 1038gRobic Nylon
Gossamer Gear Mariposa 60L34.2 oz / 968gRobic Nylon
REI Flash 55L45 oz / 1276gRobic Nylon
Gregory Focal 5841.3 oz / 1171gRobic Nylon
SWD UL Long Haul 5030.2 oz / 856gUltra 200
Durston Kakwa 5531 oz / 880gUltra 200


The REI Flash Air 50 is an ultralight rolltop backpack that weighs under 2 lbs. It’s best used for 3-5 day backpacking trips where you can fill the backpack up with food, clothing, and gear but becomes a bit awkward to use for shorter trips because it has relatively poor compression or external gear attachment capabilities. It is however a good option for extended or gear-heavy trips or travel because its lightweight frame and padded hip belt provide superb load-to-hip transfer for loads up to 40 lbs. If you want a pack with a top lid and better compression or gear attachment capabilities, we also recommend the REI Flash 55 backpack which is quite similar but has a richer and more robust feature set but weighs about a pound more although it’s still under 3 lbs in weight.

Disclosure: REI donated a backpack for review.

Shop at REI


SectionHiker is reader-supported. We only make money if you purchase a product through our affiliate links. Help us continue to test and write unsponsored and independent gear reviews, beginner FAQs, and free hiking guides.


  1. You note that the Y-strap on top could be used to hold a bear canister. Have you tried it yet? If so, how secure is the hold and how comfortable when hiking? (Does the canister bump your head?) Thanks.

    • YES – THE cord of the Y-strap fits nicely into the grooves along the side of the BV500 and it does not bump you in the head. Also a BV475 will fit horizontally in the bottom of the main compartment, while the BV500 does fit horizontally when packed at the top of the main compartment.

  2. Shorts and Microspikes

    Do you think there would be a way to rig a Y strap from the Flash Air onto the Flash 55?

  3. Think the Crown 3 weight is just for the pack without lid or frame sheet. I’d think a comparable configuration to the Flash 50 would include at least a frame sheet, so closer to 40 oz.

  4. You always do such a detailed review!
    Many of us apprecitate your careful investigation into EVERY pice of gear you review!
    Philip, will you be doing a review on the Mystery ranch Radix packs?

  5. What is the denier of this packs fabric?

  6. Curious myself, I called REI’s flagship store in Seattle and chatted with an older, experienced employee. He told me what trails below.

    Ultralightweight packs intended to carry fewer than 25 pounds are typically not made from fabrics characterized by denier. The Flash Air 50 is one of these packs, and the fabric is a multi-layer, quote, “super thin” non-denier membrane called ultra-high-molecular-weight polyethylene (UHMWPE).” It’s 87% nylon and 13% polyethylene sandwiched together in a grid pattern.

    And so there is that.

    • That’s BS – the denier part. REI just doesn’t release those kinds of specs.

      • Could be.

        After posting, because I’m a sperg or something, I looked up the UHMWPE fabric on several wholesale websites. None of them referenced denier. Instead, they used “thread count.” I assumed this is because denier indicates a bundle of threads and thread count means individual fibers and not bundles of threads.

        Dunno. However, in true sperg form and after considering your reply, I reviewed REI’s website. REI publishes denier for multiple of its in-house products like the Magma sleeping bag line. Some competitors have the means to reverse engineer REI products to determine what it is they’re made of, including fabric, assuming they’re interested in REI.

        So why would REI decide not to release denier count when some prospective purchasers, like me, and I don’t buy much through REI or even visit their stores often, would want to see the specs? I’ve sperged out enough on PP’s denier question and so will let the matter drop. Someday an answer will pop up and I’ll see it.

        Thanks for your service. A reason I don’t shop REI, although I am a member, is because websites like yours exist and I don’t need to eyeball products in person.

        • They do do it on sleeping bags, but not on down jackets, rain jackets or backpacks. I suspect its so they are not locked into fabric supplies or styles with their contract manufacturers (so they can change mid-year or between model years without changing the product name). It might also be because they sell to an audience (including me) that cares more about value and price than nerdy specs like denier – which, although it is used as a measure of durability by some people, is a pretty poor approximation of it.

    • REI responded: 70D/100D. No idea what author is on about, denier is the standard by which tent/backpack makers rate their fabrics. Likely imperfect, like pad R values but it’s what we got. Like GG packs (previous owner of 2 packs), too light for my use case, and overpriced. Seems like a good pack otherwise.

Leave a Reply

Your email address will not be published. Required fields are marked *

Captcha loading...