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REI Flash 55 Ultralight Backpack Review

REI Flash 55 Backpack Review

The REI Flash 55 Backpack is an ultralight, roll-top backpack with an optional top lid pocket.  Weighing 2 lbs 13 oz, it has a mesh back panel to help keep your shirt dry in warm weather and numerous pockets and straps, called “packmods”, that can be removed or reconfigured to lighten it further, up to 6.4 oz on our scale. The pack has two mesh water bottle sleeves in addition to two side pockets that are large enough to carry 1L bottles, a front stretch pocket, dual-side compression straps, and dual daisy chains running up the length of the pack’s seams.

Make no mistake, the REI Flash 55 is a true ultralight backpack and represents an exciting leap forward by the Co-op to make lighter-weight backpacking more accessible and affordable. Plus, at $199, the REI Flash 55 is a Best Buy. We are very impressed by the fit and carry. You can pay a lot more for a lot less when it comes to an ultralight backpack.  A Women’s REI Flash 55 Backpack is also available.

Specs at a Glance

    • Volume: 55L
    • Weight (total): 2lbs 13 oz (size medium)
    • Weight (stripped): 2 lbs 5.6 oz (size medium)
    • Gender: Unisex and Women’s available
    • Frame: Internal, Perimeter Wire
    • Adjustable Torso Length: Yes
    • Pockets: 10, including the main compartment
    • Bear Canister Compatibility: BV 500 and the Garcia Backpacker’s Cache fit vertically in the main compartment, horizontally in the extension collar, and horizontally under the floating top lid pocket; BV475, BV450, and BV425 fit horizontally at the bottom of the main compartment.
    • Torso Sizing: (S: 17-19 inches), (M: 18-20 inches), (L: 19-21 inches)
    • Hip belt Sizing: (S: 32-40 inches), (M: 34-42 inches), (L: 34-46 inches)
    • Maximum recommended load: 30 lbs
    • Materials: 100D and 210D  recycled Robic Nylon
    • Optional Add-on Pockets and Straps (available separately) – Waterproof shoulder pocket, solid-faced hipbelt pocket, mesh-faced hipbelt pocket, and extra accessory straps.

Backpack Storage and Organization

The main compartment closes with a roll top, although you can add the floating lid top pocket for more storage or organization.
The main compartment closes with a roll top, although you can add the floating lid top pocket for more storage or organization. You can also attach the end of the roll top along the sides of the pack.

The REI Flash 55 is an ultralight-style roll-top backpack with an optional top lid. The advantage of using a roll-top is that it lets you compress loads from the top in addition to the sides using compression straps. This is useful if your load expands and shrinks during a trip, like when you resupply your food in town on a thru-hike or section hike.

The Flash 55 has a floating lid pocket that can be use to hold a bear canister on top of the pack.
The Flash 55 has a floating lid pocket that can be use to hold a bear canister on top of the pack.

The nice thing about having the optional top lid is that you can add it when it’s needed, in cooler weather, for example, to carry extra gloves, navigation gear, or smaller items that are handy to have easily accessible on longer hikes.

The Flash 55 top lid is also a floating lid, which is important because the pack has a long extension collar that extends above the top of the frame. Having a floating lid lets you raise its height, so it sits properly on top of your load. It also lets you wedge gear between the top of the main compartment and the bottom of the top lid, like a bear canister, tent, sleeping pad, etc, without having to put it into the main compartment. That greatly expands the pack’s utility on more remote or technical trips when carrying awkwardly sized gear is necessary.

The sides of the floating lid extend over a BV500 bear canister for a very secure carry
The sides of the floating lid extend over a BV500 bear canister for a very secure carry

The main compartment of the Flash 55 is huge and it will hold a lot of gear and food (it feels far larger than 55L and the volume probably doesn’t account for the extension collar). It has a hydration pocket inside with a central hang loop, but the rest of the 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.

The front pocket is great for stuffing layers or a wet tent, with durable mesh side panels to help drain and dry items
The front pocket is great for stuffing layers or a wet tent, with durable mesh side panels to help drain and dry items

The Flash 55 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 also hooks onto a plastic dongle for added security. Daisy chains run along both sides of the front stretch pocket and extend up the side seams all the way to the top of the frame. These can be used to lash accessory gear to the outside of the pack, like snowshoes (MSR Lightning Ascents fit), and also serve as anchors for the side compression straps so you can move their anchor points up and down the sides of the pack.

REI Flash 55 Backpack

Comfort
Weight
Suspension
Features
Adjustability
Sizing
Durability

Ultralight and Customizable

The REI Flash 55 is a highly configurable, ultralight backpacking pack that weighs 2 lbs 13 oz but can be stripped down to 2 lbs 5.6 oz by removing several optional components. We like this pack because its so flexible and comfortable to wear, at a price that's easily affordable by anyone wanting to get into ultralight backpacking.

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The Flash 55 has side pockets for gear storage and mesh sleeves to hold water bottles
The Flash 55 has side pockets for gear storage and mesh sleeves to hold water bottles

The Flash 55 has two mesh 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 (shown above) or Nalgene Bottles (shown below) and it’s easy to pull them out. The sleeves have snap closures in front to hold the bottles in place, but they can be difficult to re-snap closed when wearing the pack. One hack to make tall bottles more secure is to lower one of the side pack mod straps so it covers the bottle’s cap.

The Flash 55 has a unique side pocket configuration with two pockets - open open mesh pocket and a solid side pocket behind it.
A 1L Nalgene also fits snugly in the mesh water bottle sleeves.

The Flash 55 also has solid paneled 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. Note: you can run the side packmod straps over these side pockets or through them.

There are four removable pockets on the Flash 55, all of which are optional.  The top lid is attached by buckles and can be easily removed, as well as the straps holding it to the pack. These straps can be repurposed for other functions and at other locations on the pack.

The hipbelt pockets are huge and capable of carrying electronics and food.
The hipbelt pockets are huge and capable of carrying electronics and food.

The hip belt pockets are also easily removable. One is mesh-faced and the other has a solid fabric front. They’re quite large enough and big enough to hold my iPhone 14 Pro plus snacks. They’re held on with a clever webbing strap/toggle system that holds them in place and prevents them from flopping as you bounce down the trail. It is yet another example of the “packmod” philosophy behind this pack’s customization ethic.

It’s a wonder that more ultralight backpack manufacturers don’t adopt a similar pocket attachment strategy, since people have very different needs at different times. I prefer having a choice over which pockets to attach to my backpack instead of being forced to use one that is permanently affixed.

The pockets are attached using a simple webbing and plastic dongle attachment system
The pockets are attached using a simple webbing and plastic dongle attachment system

The Flash 55 also comes with a mesh shoulder strap pocket that’s attached to the shoulder pads using the same webbing/toggle system used by the pockets. It’s sized narrow for a Smartphone, an inReach  Mini 2. or a small camera. It is secured on top with velcro. Earlier models of the Flash 55 has 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 Flash 55 comes with a mesh shoulder strap pocket which is also removable.
The Flash 55 comes with a mesh shoulder strap pocket which is also removable.

Backpack Compression and External Attachment System

The stock REI Flash 55 comes with an elaborate but easy-to-use compression and external attachment system. You can use it out the box, as-is, remove the numerous straps (without having to cut them off), or move them around any way you need.

All of the PackMod straps attach the daisy chains running along the pack sides. You can also attach other gear.
All of the PackMod straps attach the daisy chains running along the pack sides. You can also attach other gear.

The four vertical corners of the pack have daisy chains loops running down them, implemented using cord, instead of traditional webbing. This is an increasingly common feature found on trail running backpacks, but it hasn’t really caught on yet with mainstream ultralight backpacks.

All of the straps and attachment points on the pack are loops (girth hitched) to the daisy chain instead of being sewn into the pack seams. This lets you detach them, move them to a different location, or change their angles, as needed.

REI even includes a mesh sack with the Flash 55 so you can store the straps you’ve removed between uses, and not lose them. Directions for attaching the straps are printed on the outside. Thoughtful.

The Flash 55 includes a stuff sack for storing removed packmods when not in use.
The Flash 55 includes a stuff sack for storing removed packmods when not in use.

All of the removable straps and pockets weigh 6.4 oz on our scale. If you’re trying to reduce your pack weight, the biggest bang for the buck comes in removing the pockets, not the straps.

  • the floating top lid w/2 straps (3.3 oz)
  • 4 side compression straps (0.8 oz)
  • solid hip belt pockets (0.8 oz)
  • mesh hip belt pocket (1.0 oz)
  • shoulder strap pocket (0. 3 oz)
  • 2 additional short straps (0.2 oz)

The problem with removing the side compression straps is that you often can’t anticipate when you’ll need them to lash gear to the side of the pack. If you remove the top lid, you can get rid of up to four straps, though I’d still recommend keeping two of them to hold down the sides of the roll top. There are a lot of variations possible, though.

Backpack Frame and Suspension

The REI Flash 55 is an adjustable-length backpack with a mesh back panel to help keep you cooler and your shirt drier in warm weather. The torso length is dead simple to adjust, by moving the shoulder strap yoke up or down horizontal webbing straps arranged down the middle of the back panel and labeled in inches for ease of fit if you already know your torso length. See how to measure torso length. 

The torso length is adjusted by moving the shoulder yoke up or down.
The torso length is adjusted by moving the shoulder yoke up or down.

The back panel mesh is stretched across soft dorsal and lumbar padding and integrated with the pre-curved wings of the hip belt. This provides a comfortable back-hugging fit, but won’t pull you backward and off-balance. While it’s not as breathable as a curved ventilated backpack like the Zpacks Arc Ultra Haul 60 or the Osprey Exos Pro 55, it does a pretty decent job at helping you stay cooler drier in hot and muggy weather.

The backpanel is covered with mesh so it won’t stick to your back when you perspire.
The back panel is covered with mesh so it won’t stick to your back when you perspire.

The Flash 55’s frame is a lightweight, 360 degree 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 55, which is comfortable and does not slip down.

The hipbelt is exceptionally well padded with precurved wings
The hipbelt is exceptionally well padded with pre-curved wings that provide a no-slip grip.

The hip belt closes with pull-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 a unisex J-shape, with a rail-based sternum strap. They’re thickly padded and covered with a breathable mesh to wick away sweat. Both shoulder straps have elastic hose keepers as well as a pair of short horizontal webbing straps to attach the shoulder accessory pocket, which can be easily moved to the other shoulder strap.

The sizing ranges for the men’s Flash 55 pack are quite narrow in terms of torso lengths although the hip belt sizing is more flexible. Still, I’d encourage you to try on different sizes to zero in on a comfortable fit. If you’re between torso lengths, I’d definitely recommend sizing up.

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

Recommendation

The REI Flash 55 is a highly configurable, backpacking pack that weighs 2 lbs 13 oz but can be stripped down to 2 lbs 5.6 oz by removing several optional components. If you’ve never owned a backpack that’s this lightweight, the Flash 55 is a good ultralight pack to cut your teeth on because it’s so affordable and easily customized for different trips, seasons, or locales. Fully configured, out-of-the-box, with its top lid and full compression system, you can use it as long as you don’t exceed its maximum recommended load of 30 lbs or gear, water, and food weight. If you want to experiment with removing the lid and just using the roll-top, or removing components, you can do that when you’re ready. Regardless, I think you’ll still be impressed at how well the Flash 55 carries compared to a heavier-weight backpack with a more substantial frame. This pack is a winner.

Disclosure: REI donated a backpack for review.

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25 comments

  1. So this is an updated version? What are the differences between this and the one you reviewed a few years ago? It looks like the adjustable torso length is new.

    I have used the first version in medium and would really like to purchase it because the hip carry is excellent, as you mention in your review. The shaping of the lower back and hip foam is really well done to prevent the pack from creeping down. However, the medium torso length is a bit too small for me while the hip belt on the large is too long and won’t tighten adequately, so the first version did not work for me. I will have to try out the new version.

    • It’s the updated version. The biggest difference is the adjustable length torso. They also switched to lighter-weight fabrics, changed the stock packmods a bit, and modified the sizing slightly.

      • It’s funny that they switched to lighter weight fabrics, but the overall weight is more than the previous version. I don’t like the new phone pocket and the brain is no longer waterproof. The only thing improvements I see are the adjustable torso and exchangeable hip belt. Love the previous version, not sure about this one.

  2. I have the original version but I am on the lower end of the waist size medium. I love the pack but it keeps slipping down my waist. too bad that the smallest waist size of this pack is a 32.

  3. I’m going into year 3 with my Flash 55 and I love it. I don’t use the phone pocket because it was too cumbersome and in an uncomfortable position on my chest. I also like the adjustable sternum strap with built in whistle. I don’t use it all the time but I like that I can slide it up and down the shoulder straps and that it has elasticity so I can take pressure off certain areas for a while. I see they changed the back pocket which is all mesh on the original and holds quite a lot, so not sure if that was an improvement. I also jerry rigged the packmod pockets so they sit more anteriorly on the hip belt as I didn’t like my arms brushing against them when they were sitting more on my hips. Apparently I have a short torso as I’m 5’5” but was fitted for an XS pack. I have never used the brain, but will be required to carry a bear canister on a thru hike I have planned this summer so I appreciate that carrying tip. However, the pack has so much room I could probably carry it inside and still have room for my other gear. I love all the exterior pockets and how easy it is for me to access my water bottles while hiking. I’ve carried a max weight of 27 pounds very comfortably with it. It’s a very durable pack too…I almost wish it wasn’t because I like the new color options. Thanks for a great review.

  4. I’ve had mine a few years, really like it. Not the lightest, but ‘relatively’ light and inexpensive. Good compromise for someone like myself that wanted to reduce weight, but not break the bank. :-)

  5. Mikhail Ruslan Barson

    I went through 2 versions of Flash 55 over the last 4 years. I have atleast 8 other packs I prefer above it right now, but as for the way it carries it is at the very bottom of my list. It is practically structureless making a small amount of gear feel several times heavier and just hang on the shoulders compared to a similar weight Osprey or Gregory or even a Deuter. I have packs several times heavier that make even heavier hauls feel negligable. If you are carrying an ultralight quilt, a rain jacket and a change of underwear its fine, anything more than a couple pounds you will need a better engineered pack….forget the bear cannister. You need a pack that will “bear” more than an extra couple pounds.

  6. I just returned from a 4 day backpacking excursion on Cumberland Island, GA. As its flat and we were luxury camping we take a lot of extra gear, chairs, saws, binoculars, etc. All 4 packs had 32-34 lbs. Three used the Flash 55. I used a GG Gorilla 50. Despite the overload, the Flash was a better carry due to better conforming hipbelt and buckle system; load lifters kept the pack much closer to the body than the Gorilla without load lifters. The lighter Gorilla is good with less than 30 lbs. But still the Flash hipbelt is more structured and rides better, similar to Gregory big pack hipbelts. Thinking I will swtch to a Flash when my local store gets them.

  7. I purchased Flash 55 recently and loaded it up for a test drive. I have 20 inch torso and 34 inch waist. REI store put me in medium sized pack. I really like the features of the pack. Simple things that you would think other manufacturers would have included. However, the one really annoying part for me is the shoulder yoke area. The pads which are part of the adjustable torso stick out farther than the pads which hit you in the middle of the back. As a result, there’s steady pressure on my shoulder blades. After about an hour of hiking, it was really annoying and somewhat painful. Is that something you’ve also experienced? Would a large sized frame make a difference? I’m leaning towards returning in favor or Exos or Focal.

  8. Excellent review
    Please could you include a link to your review of the older model
    I purchased the older model because of your review and would be happy to see it again
    thanks

  9. Thank you for all your reviews! I was wondering how you think the flash fit compares to the Gg gorilla? I purchased the gorilla after much research and the fit is just not comfortable for a female (5’7” small shoulders, curvey hips). The shoulder straps rub my neck, and the hip belt does not stay on curvy hips, back panal rubs on low back. REI measured me before the purchase, so I believe I bought the right size (medium). I am upgrading/ replacing an old Lowa alpine which was amazingly comfortable carrying all sorts of kids gear. Planning to backpack this summer. Thank you for your time!

    • It’s hard to know how the pack will fit you without seeing you with the pack on, but I like the fact that this new version has an adjustable torso length because that makes all the difference. The Gorilla isn’t for everyone and the fixed torso length doesn’t help.

  10. I’m in the market for a 40-50ish liter pack and have narrowed it down to the Zerk 40 and this guys. Obviously, different types of packs but both have big pluses and minor quibbles. I’m more of a weekend warrior type but want something comfy while allowing me to pack some of my kiddos gear. My base weight is about 9lbs… Which of those two would you suggest for that type of scenario?

  11. If you’re carrying your kids gear, I’d get the REI pack.

  12. In your first picture (top-down perspective), you have a strap running over the top of the pack. Did you relocate a strap from elsewhere on the pack or buy it extra? I just bought the same pack and it does not have that top strap.

  13. You said in your review that you can attach the ends of the roll top along the sides of the pack. Could you clarify how? I’m trying to do this but don’t know what to buckle them into.

  14. How would you compare this to the Granite Gear Crown 3? Which would you choose for a starting load (including pack) of 30-35 lbs for a colder weather trip?

    • If you plan to lash gear to the outside of the pack, I’d go with the crown, simply because the straps are positioned at the right place to attach pads or snowshoes without fiddling arround. Otherwise, they’re both pretty similar packs.

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