REI Flash 55 Ultralight Backpack Review (2024)

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.

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 BV425fit 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 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 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 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 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.

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 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 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 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.

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.

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.

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 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 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 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

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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