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REI Co-op Flash 45 - Women's Review

The REI Flash 45 is a noteworthy ultralightweight pack if it fits.
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Price:  $160 List | $159.00 at REI
Pros:  Super light-weight, customizable compression straps, removable brain.
Cons:  No torso adjustments, hip belt is uncomfortable, not bear-can-compatable.
Manufacturer:   REI Co-op
By Meg Atteberry ⋅ Review Editor  ⋅  May 8, 2019
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#12 of 17
  • Comfort and Suspension - 45% 7
  • Organizational systems - 20% 7
  • Weight - 20% 9
  • Adjustability - 15% 6

Our Verdict

As one of the lightest packs we tested, the REI Flash 45 is built for the no-frills woman backpacker. Its simple design integrates the ability to move straps around and make the pack work for your kit. However, the Flash lacks any sort of adjustment system in the suspension of the pack, so it either fits, or it doesn't. With so much hinging on limited sizing options, this pack fell short in a lot of ways for us. However, if you're one of the lucky few who fit this pack, it might just be your Cinderella slipper for your backpacking needs.

Compare to Similar Products

Our Analysis and Test Results

Performance Comparison

The REI Flash 45 stood out when it came to weight. For a little over two pounds, you get a removable brain, plenty of compression straps and a roomy main compartment for a 45-liter pack. Overall we loved some of the features on this pack, but it's lack of adjustability meant that it chaffed and didn't fit quite right, leaving us plenty sore and bruised the next day. The smaller pack volume also means that your adventure options are limited.

The Flash 45 is a super-lightweight  minimalist pack that has just enough room for a weekend on the trail  but the lack of adjustability means it has to fit you perfectly as-is.
The Flash 45 is a super-lightweight, minimalist pack that has just enough room for a weekend on the trail, but the lack of adjustability means it has to fit you perfectly as-is.

Comfort and Suspension

Unfortunately, this was one of the least comfortable packs we tested, mostly because you can't adjust the pack. Essentially, you buy one of the limited size offerings, and it either fits or it doesn't. This strategy was chosen to save weight on the overall design, but when you are a half inch between sizes, this is the difference between chafing and not. Hip belts and torso heights aside, the back panel offers a mix between mesh and foam padding, which does a decent job at keeping moisture at bay. If you want the most sweat-free pack, check out the Aura AG. For such a minimalist pack, we were impressed by the Flash's thick and well-padded shoulder straps.

The Flash also has an ultra-light Activflex LT wireframe that keeps the pack rigid when weighted down. The suspension system doesn't do the best job at delivering the pack's weight to your hips; our testers had sore shoulders after testing. However, this might be because the tester was in between sizes.


At just a hair over two pounds, the Flash is one of the lightest packs in our lineup. However, without any adjustment systems, we felt that REI went a bit too far with this one. Trimming out any options for adjustments in the suspension system didn't do any favors to win us over with this pack. For five ounces more weight, you can wear the Granite Gear Blaze 60 that not only offers 15 additional liters but is also adjustable to fit your back.


When it comes to features, the Flash 45 offers some great opportunities to adjust your kit. For example, The Flash offers an array of attachment points for compression straps that offer a wide variety of configurations to fit your needs. REI also advertises this pack as coming with two additional straps (although these did not come with the pack we tested). This setup allows for a range of adjustability that makes this smaller-volumed pack work with you better than say the Osprey Kyte 45. Where the Flash misses the mark is with fit adjustability. It simply doesn't exist. There is no way to extend or shorten the torso height, so you either fit into one of the three offered size options, or you don't. Our tester fell between sizes and ended up with bruises and chaffing after one day of use.

In order to save weight  the Flash 45 doesn't have any torso or hip belt adjustments.
In order to save weight, the Flash 45 doesn't have any torso or hip belt adjustments.

Organizational Systems

The simple nature of the Flash means that there are not a lot of extraneous pockets. There are two exterior side pockets (non-zippered) on each side of the pack that helps hold a tent or shelter, an extra layer, as well as a water bottle. There is also an additional, roomy mesh pocket on the front of the pack, as well as a fairly spacious (and removable) pack brain.

The main compartment only has one access point through the top. We didn't find this to be too cumbersome, as long as you packed thoughtfully. This pack may present a few challenges for the beginner backpacker, but once you have your packing order nailed down, you can quickly get things in and out of the pack. The small pack volume of the Flash means that this pack doesn't play well with extra items such as helmets, ropes, and bear cans. This pack is best suited for the straight-up backpacker that doesn't need any special gear and has a more streamlined setup.

The Flash 45 makes quick work of a lieghtweight backpacking setup and has just enough rrom for a quick overnight.
The Flash 45 makes quick work of a lieghtweight backpacking setup and has just enough rrom for a quick overnight.


REI offers one of the more transparent sustainability reports in the outdoor world. They regularly produce Product Sustainability Standards that offer an in-depth look at materials, suppliers, and labor.

REI also offers a stout repair program, along with their signature garage sale, where you can purchase gently used items. However, you must be a member to utilize these programs.

Best Applications

The REI Flash 45 is best suited for the warm-weather backpacker who is simply looking for shorter, more straight forward outings. Beginners may struggle a bit at first, especially if they have a bulkier kit. However, gram-counting enthusiasts will love the pack's low weight and customizable compression straps. If you've got a streamlined kit and want something light and fast, this pack may be for you, but make sure you try before you buy because the sizing is a huge concern.

If the Flash 45 fits you  then it's the ideal choice for an ultra-lightweight  overnight backpacking pack.
If the Flash 45 fits you, then it's the ideal choice for an ultra-lightweight, overnight backpacking pack.


The Flash falls under $170, making it one of the more budget-friendly options for a lightweight backpacking pack. You get quite a fair amount of bang for your buck with this pack, but if you want a few more options (and more space) you might want to consider the Osprey Renn 65 or the The North Face Terra 55.


At a great value, the REI Flash 45 is a great, no-frills pack if the torso fits you. If not, we recommend checking out a few of our higher-rated, budget-friendly models.

Meg Atteberry