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REI Co-op Flash 18 Review

A simple pack that's easy on the wallet, ultralight, and super popular
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Price:  $40 List | $39.95 at REI
Pros:  Affordable, minimalist design, lightweight, super packable.
Cons:  Few features, thin shoulder straps and hip belt.
Manufacturer:   REI
By Dan Scott ⋅ Review Editor  ⋅  May 13, 2019
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#9 of 16
  • Comfort - 25% 5
  • Weight - 25% 10
  • Versatility - 25% 6
  • Ease of Use - 15% 7
  • Durability - 10% 4

Our Verdict

We've owned a Flash 18 since the pack debuted in the late 2000s. We've used it in most environments under most weather conditions, ranging from day hikes to long, multi-pitch climbs and everything in between. Its low price, super low weight, and superb simplicity mean that we'll likely own a version of this pack for a very long time. This pack is a minimalist's dream and scored highly in weight and versatility. With a simple top-loading design opening into a single compartment, this pack remains comfortable during a myriad of activities. It's less hiking specific than any other we tested, but it can most certainly transition between activities. This is an especially good choice if you're on a budget and need a pack to take you from urban life to the mountain then to the crag. This pack climbs well due to its narrow profile and is an excellent option for multi-pitch days and summit attempts.

Compare to Similar Products

Our Analysis and Test Results

Performance Comparison

Check out the REI Flash 18 for one of the most versatile packs we tested, at a price you can't refuse. It carries light loads securely, is easy to stuff and dump out quickly, and can easily find its way on all but the most gear-intensive adventures.

The Flash is the daypack of choice for this Great Dane.
The Flash is the daypack of choice for this Great Dane.


This pack sits comfortably on your back as long as you don't overstuff it. Due to the frameless back panel, it is easy to overload, causing the back paneling to round. The shoulder straps are thin and breathable but are the first source of discomfort when weighing this pack down with anything over 10-15 pounds. Unlike the very similar Flash 22, the shoulder straps are not padded, which turns out to make a big difference in comfort. This is an essentials-only type of pack. If you want a pack to carry more gear more comfortably, look for packs with more robust suspension

The flash fits most people  from our lead tester (pictured here; 6'5"  225 lbs)  to his smaller partner (5'5"  110 lbs).
The Flash 18 is one-size-fits most  and it really does. It fit both this 5'5"  110 lbs tester  and our lead tester  who is 6'5"  225 lbs.

The Flash is a one-size-fits-most pack, but we found that across a range of torso sizes, from a 5'5" tester to a 6'5" tester, we could cinch the suspension down tight on the shoulders for bouncy trail running, or let some out and get the weight at least partly on the hips for hiking. When cinched down, it didn't bounce and hugged the torso well, making it ideal for long runs.

One useful tip is that you can remove the light padding in the back of the back and use it as a cushion on your lunch break. If you happen to be looking for a little more structure in the back paneling, you can easily replace this foam with a stiffer version. Even a Sam Splint works great (and then you're doubly prepared).

Weight-to-Volume Ratio

You can't beat the low weight and low price of this bag. Weighing just nine ounces, it has a super low weight to volume ratio of 0.51 oz/L. Other packs provide more features, but only rarely does a pack match the Flash 18's low weight.

Ultralight packs are great for light loads  but don't offer much ventilation or stability.
Ultralight packs are great for light loads, but don't offer much ventilation or stability.


Due to the lightweight, minimalist design, this pack has versatility beyond a typical daypack. One of our testers ran the Grand Canyon from rim-to-rim and back with a version of this pack and found that it worked well.

The Flash 18 also works great for bike commuting or climbing and packs down to about the size of a softball. This small size makes it easy to bring on longer backpacking trips or travels as a separate daypack. In this scenario, it can be used as a stuff sack inside a larger pack, and then removed to use as a summit pack when needed. If you don't plan on using it this way, then perhaps you should consider if this feature is worth the loss of comfort and ease of use.

The top loading design lets you accommodate bulky items that can be hard to pack into panel loading designs.
The top loading design lets you accommodate bulky items that can be hard to pack into panel loading designs.

Ease of Use

The Flash 18 is a relatively simple pack but has what you need for many different adventures. It is hydration compatible and also comes with an external pocket including a key clip for stowing smaller items. It has a daisy chain fixed to the outside for extra external carry options, such as clipping your shoes on. There are four perimeter loops next to the back panel that you can clip things to, or use to secure cordage for extra lashing options. The base of the daisy chain has a loop for an ice axe, and you can connect the top with a ski strap or Velcro loop.

This pack is simple: just one zippered outer pocket plus the main compartment. However  it gets the job done.
This pack is simple: just one zippered outer pocket plus the main compartment. However, it gets the job done.

The waist belt offers some stability, but the thin webbing becomes uncomfortable with heavier loads. The sternum strap does come equipped with a whistle. However, on larger torsos, it does not lower enough on the shoulder straps for a proper fit and can make you feel as though you're being choked. The good news is that both of these features are detachable. Unlike past versions of this pack, this model has nylon carry loop at the top. This makes it slightly easier to clip into the anchor if used for multi-pitch rock climbing.

The side opening front pocket was a really convenient place to store items while traveling. Just be sure to watch your back!
As you can see  the main compartment now features two small stuff pockets sized perfectly for a phone or keys.

A 14-inch laptop will fit into this pack. However, the bag does not provide much protection for any device, other than a thin foam pad. While it is hydration compatible, a three-liter bladder takes up most of the space in the small bag.


This year's Flash 18 performed surprisingly well in our hose test. The fabric shed water well, but of course let in drips through the cinch top. The cinch flap kept contents dry for a little while, but we think of this pack as being more ideal for drying quickly than keeping things dry.

We also lightly tested how much snow can work its way in through the gap created with the drawstring. During our test, the pack remained snow free, but more rigorous activity in a harsh storm would almost certainly allow snow and ice to come through.

Whether an avid hiker  or just playing around in the mountains  the Flash 18 is ready for anything.
Whether an avid hiker, or just playing around in the mountains, the Flash 18 is ready for anything.

Through months of testing, including bushwhacking through dense foliage in Red Rocks National Conservation Area, the pack survived without noticeable wear. On a side note, however, one tester hauled an older version of this model up 90 feet on the Diamond of Long's Peak. It scraped its way up, snagging along the way, and eventually arrived at the belay battered and torn, but was still usable. For what it's worth, that version and the newest version seem to be made of the same material. The Flash packs are also remarkably easy to repair, having very simple construction. Just clean it up, slap on some tape, and it's good to go.


The Flash 18 is the least expensive of the packs reviewed, but also the least durable for rigorous backcountry conditions. We find that it provides the excellent value for the dollar. Not only is this pack super versatile and lightweight, but it is also backed by the REI 100% satisfaction guarantee.


For the weight and price, this specialized and compact pack deserves your attention. The super simple design is ultralight and very inexpensive. Other packs are more durable and supportive of heavy loads, but for smaller missions and for tucking into the corner of your bigger bag, the Flash 18 is unique.

Dan Scott