REI Co-Op Flash 55 Backpack Review (I Tested the New Model)

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REI Co-Op Flash 55 is best for:

• All skill levels, including new backpackers given its user-friendly features
• Trips of varying lengths 
• Ultralight enthusiasts on a budget

REI Co-Op Flash 55 might not be a fit for:

• Thru-hikes without ultralight gear given its 30-lb (13.6-kg) load capacity 
• Extremely rough terrain due to areas of mesh fabric 

With brutal honesty, I’ve rated the REI Co-Op Flash 55 4.8 out of 5 stars. As one who falls outside a standard adult build, I love that it’s available in gender-specific models and various sizes. This improves not only the backpack’s aesthetic but its comfort. The same applies to its easy-to-use, adjustable back panel. 

As a whole, the eco-friendly pack is very user-friendly, as well as lightweight, durable, and water-resistant. Its interior is spacious, and it has several external organization features. You can also customize the pack to your preferences with its Packmod system. 

Priced at $199, I think this pack comes at a pretty good value. However, if you want a complete kit, you’ll need to pay a bit more. For example, the REI Flash 55 doesn’t come with a rain cover. The brand recommends pairing it with the medium REI Co-Op Duck’s Back rain cover, which will set you back another $29.95.

Also, if you don’t have the most ultralight backpacking tent, you’ll want to invest in a set of Packmod accessory straps, which cost $9.95. Reason being, the pack lacks base straps, and storing your tent vertically in the main compartment isn’t very comfortable.

In addition, the REI Flash 55 has a somewhat unclear warranty. Depending on the web page you pull up, its manufacturer guarantee may last a lifetime or exactly zero days after purchase. It’s also unclear how you’ll be compensated if a product defect were to become evident. 

But remember, my job is to nitpick and overall, these issues are minor. Assuming your pack arrives in great condition, and aside from maybe a couple of extra purchases, the REI Flash 55 is a great backpack choice. I love this product for so many reasons, namely for its customizable features and performance on the trail. 

If the REI Flash 55 doesn’t quite meet your requirements, see the Alternatives section. I overview two other personally-tested packs that might better fit your needs.

Video Review REI Co-Op Flash 55

You can keep scrolling for my detailed REI Co-Op Flash 55 review.

Or  click play on my video review rounding up the  8 top backpacking backpacks I compared on our trip in Utah.

(Note: the Gregory Maven section starts at 05:19 in the video).

REI Co-Op Flash 55 Features Review

That’s the quick summary of this REI Flash 55 backpack review. But there’s so much more to be said about this pack. 

Below, I explain what exactly makes this product both durable and lightweight. I’ll also describe its user-friendly features and how to make the pack custom to your preferences. This includes an overview of its unique pack mod system — and how it provides a solution to one thing I didn’t love.  

I discuss the following features in this in-depth section:

Size

⭐ STAR RATING: 5 / 5 stars

The REI Co-Op Flash 55 is available in gender-specific models, as well as various sizes. As someone who falls outside of a standard adult build, I appreciate the selection. Unlike “one size fits all” packs, this bag not only looked appropriate for my size but fit very comfortably. 

The extra small women’s model has a volume of 53 liters. I packed roughly half of the gear pictured above and still had space for additional items. Some may not find this pack to be spacious enough for long thru-hikes, especially given its 30-lb (13.6 kg) load capacity. But it’s absolutely suitable for multi-day trips. 

To understand how its 53L is distributed, I took inspiration from ASTM International. Its standardized test for determining backpack volume involves measuring with plastic balls. So, I ordered hundreds of golf balls and found that roughly 12 golf balls equate to a liter. Here are my findings:  

• Lid – 83 golf balls / 6.9L 
• Front pocket (with the main compartment empty) – 130 golf balls / 10.8L
• Primary side pocket (2x) – 38 golf balls / 3.2L
• Mesh side pocket (2x) – 20 golf balls / 1.7L
• Hip belt pockets (2x) – 11 golf balls / 0.9L 
• Shoulder pocket – 6 golf balls / 0.5L 
• Accessory pocket – 40 golf balls / 3.3L 

With this math, the main compartment is around 23.7L. However, as noted above, the front pocket measurement was taken with the pack empty. If this pocket weren’t filled to its max capacity, you could trade some of that volume for main compartment space. 

It’s not a perfect science. But hopefully, more than anything, this gives you a rough idea of how the PackMod accessories influence capacity. See the External Organization section for more info. 

Weight

⭐ STAR RATING: 5 / 5 stars

Even at its heaviest (men’s large size), the REI Co-Op Flash 55 weighs just 2.875 lbs (1.304 kg). The version that I tested (women’s extra small) weighs an impressive 2.625 lbs (1.191 kg).

Most experts would agree that your pack shouldn’t weigh more than 20% of your body weight [ Source]. I’m a 100-lb (45.4-kg) individual, and a 20-lb (9.1-kg) load can be quite limiting. I appreciate that this lightweight pack doesn’t take much away from my maximum carry capacity. 

👉 FYI: For its size, no other backpacking pack I tested weighs less than the REI Flash 55, except for one. The black model of the Hyperlite Mountain Gear 3400 Southwest clocks in at just 2.2 lbs (0.979 kg).

Height Adjustable

⭐ STAR RATING: 5 / 5 stars

The REI Flash 55 is incredibly user-friendly, and its height-adjustable feature is no exception. Simply un-velcro the back panel and shift this up or down to accommodate your torso length.

There are even printed instructions on the pack, which direct users to secure the panel through three loops. The max and minimum torso lengths are also printed.  

The women’s extra small pack that I tested has a range of 15-17 in (38.1-43.2 cm). For all sizes’ torso measurements, see the Technical Specifications section.

Comfort

⭐ STAR RATING: 5 / 5 stars

The REI Flash 55 is incredibly comfortable, despite being a lightweight backpacking pack. It features a cushioned, breathable mesh back panel. The shoulder straps and hip belt are also well-padded, and the contoured shape of the hip belt adds stability. 

The pack has several compression straps which further support load transfer and balance. This includes the hip belt strap, sternum strap, and Packmod compression straps. 

Instructions on how to use these Pack-mod straps are printed on the included mesh pocket. Essentially, you’ll want to draw these through the daisy chains found throughout the pack. Then, tighten the straps to the shape of the pack’s contents to keep gear from shifting during your trek.  

Internal Organization

⭐ STAR RATING: 5 / 5 stars

The REI Flash 55 has few internal organization features, which is what most backpackers prefer. The spacious main compartment allows you to stuff your gear to your liking.

A hydration sleeve is found against the back panel. Hold the hydration bladder in place with the simple hook-and-loop fastener (think Velcro). Then, draw the hose through either the left or right hydration ports set on the upper back side of the pack. 

It”s unusual to see two ports for this purpose, and REI doesn’t specify this design choice. But arguably, it better accommodates both left and right-handed individuals. 

To secure the main compartment, you’ll use the pack’s unique roll-top closure. It”s similar to what you see on a dry bag and aids in water resistance. 

External Organization

⭐ STAR RATING: 4.5 / 5 stars

The REI Flash 55 has several exterior pockets, compression straps, and loops for storing gear. On the front face of the pack, there’s a large pocket that’s secured with a buckle. Elastic at its opening further helps to keep items in place. 

At the base of the pack, you’ll find an attachment loop. This is a great place to store an ice axe or trekking poles. Side compression straps also accommodate bulky gear.

However, I was disappointed that the Flash 55 lacks base straps for storing a backpacking tent. This forced me to store Skycie’s Big Agnes tent vertically in the main compartment — which isn’t particularly comfortable. 

Fortunately, REI’s Packmod system makes this easy to fix for $9.95. With attachment points at its base and hip belt, you could connect these accessory straps for external tent storage. Still, I wish the solution weren’t sold separately.  

The top lid of the pack has a spacious zipper pocket, which can only be accessed externally. I recommend keeping essentials like a headlamp and first aid kit in this easy-to-reach compartment. Four pockets on the sides of the pack grant even more quick-access storage.  

The two mesh water bottle pockets feature snap closures and are angled forward. This allows you to remove and replace a bottle without removing the pack. However, it’s difficult to reattach the snap closure with the pack on, especially if using a larger bottle like those by Nalgene.

If storing water bottles here, I’d recommend skipping that step. The pockets are deep enough for them to be secure regardless. But the snap closures are a nice touch, allowing you to store smaller items here, too — like the Katadyn water filter pictured above. 

In addition, the REI Flash 55 has removable, zippered hip belt pockets. One features a mesh face while the other is solid fabric. The more protected pocket is ideal for electronics, though it”s not quite large enough for my Otterbox-protected iPhone.  

The shoulder strap pocket, however, works well for my clunky mobile device. However, the face of the shoulder strap pocket is mesh, so make sure to remove any electronics from here when it rains or snows. REI actually suggests storing a rain cover in this pocket. 

Lastly, the REI Flash 55 comes with a small mesh drawstring bag. It’s intended to store Packmod system accessories. Instructions on how to use the Packmod compression straps and hip belt pocket are printed on it. But, of course, this bag can be used for a variety of other purposes, too. 

Removable Lid

⭐ STAR RATING: 5 / 5 stars

Several competing packs, like the Osprey Eja and Gregory Maven, have removable lids. But like other features on the REI Flash 55, this process is much more user-friendly.

Rather than straps, its lid is removed simply by clicking four side release buckles. If you’re ultralight backpacking, this is an easy way to cut down on weight. Alternatively, you can turn the lid into a waist pack by using the included Packmod straps. Extra points for versatility!  

Materials

⭐ STAR RATING: 5 / 5 stars

The primary shell of the REI Flash 55 is a 100-denier recycled nylon Robic ripstop. Similarly, its secondary shell is 210-denier recycled nylon Robic featuring high-tenacity yarns. 

The key difference between these two fabrics is their denier. This refers to how thick the fabric is, with higher numbers indicating greater thickness, and therefore, greater weight. 

Otherwise, these shells are very much the same. Robic is a proprietary nylon fabric, which in this case, is recycled. Its square grid creates a ripstop quality, meaning that if you puncture the fabric, it won’t unravel and continue tearing. 

To further increase durability, both fabrics have a PU-coated backside. This proprietary coating is called UTS (Ultra Tear Strength). Along with greater abrasion resistance, this coating helps protect against moisture. The DWR (durable water-resistant finish) on the front side of the fabric serves the same purpose. 

Hardware

⭐ STAR RATING: 5 / 5 stars

Though plastic, the pack’s side release and adjustable strap buckles feel strong and secure. The same can be said of the cord lock on the drawstring bag, and the attachment points of the removable hip belt pockets. 

The plastic sternum strap whistle is also high functioning. The metal zippers glide smoothly and the snap closures on the side mesh pockets perform well, too.  

One of the key differences between the former REI Flash 55 and the current model is stronger daisy chains. Not having tested the previous version, I can’t speak to this comparison personally. But I found all web lash points to be reliable in my testing. Though, I’d recommend being judicious and not storing anything too particularly heavy on these external features.   

Aesthetic

⭐ STAR RATING: 5 / 5 stars

Of course, style is always subjective. Though, many outdoor enthusiasts would agree that the REI Flash 55 looks pretty cool.

For one thing, it’s designed to fit your unique body type. With gender-specific models and various sizes, the pack won’t look too big or small — and therefore, will feel more comfortable, too. 

I’m biased, as yellow is my favorite color, but this vibrant tone also serves a great function. It’s the first color to catch the human eye and stands out in any natural environment. Even if you and your hiking partner set different paces, you’ll be easy to spot with this backpack.

If yellow’s not your jam and high visibility doesn’t matter much to you, the REI Flash 55 is also available in Jasper Green. It’s a touch darker than a seafoam shade, with lime green accents on the attachment points. 

In fact, both color options feature varying tones, along with multiple styles of fabrics. Mesh and straps add dimension, and the straps tighten and tuck to create a seamless look. 

Warranty

⭐ STAR RATING: 4 / 5 stars

At this point in the review, you know that I’m a big fan of the REI Flash 55. But in my opinion, here’s the backpack’s biggest pitfall: its warranty. 

REI gives a “100% satisfaction guarantee” to its customers — “with a few exceptions.” In my opinion, “few” is an understatement. In researching REI’s warranty, I had to click on multiple web pages full of legal jargon that, at times, seems to contradict itself.

For example: 

• Returns & Exchanges – This page states, “If you are not satisfied with your purchase, you can return it for a replacement or refund—with a few exceptions—within one (1) year of the purchase date if you are an REI Co-op Member or within 90 days of your purchase if you are not a member.”
• Return Policy Exceptions – This section states under Product Defects, “If your item has a manufacturing defect in materials or workmanship, you can return it at any time, regardless of purchase date.”
• REI Terms of Sale (Part Two) – Section 9 overviews the limited warranty for REI-branded goods (e.g. the Flash 55 backpack). It states, “REI warrants that new REI-branded products will be free from defects in materials and workmanship at the time of sale.”

If you skimmed that section, I don’t blame you. It’s tedious to read that kind of language, and in my opinion, this information shouldn’t be so convoluted. Are manufacturing defects under a lifetime warranty, or guaranteed absolutely zero days after “the time of sale”? 

Though the warranty period is unclear, the rest of the conditions are pretty standard. The company states that it may require proof of purchase. It may replace the item, issue a store credit, or provide a complete refund that REI determines “in good faith is appropriate in the circumstances.” 

These terms are loose and arguably more beneficial to the company than the consumer. But if you were to notice a manufacturing defect, I would lean into REI’s most generous claim — “return it at any time, regardless of purchase date.” Just keep in mind that normal wear and tear, misuse, and improper storage are not valid reasons to claim its warranty. 

Value

⭐ STAR RATING: 4.5 / 5 stars

If you’re looking for a lightweight backpack, the REI Co-Op Flash 55 is a stellar value. Several of the packs I tested were under 3 lbs (1.36 kg). These included the Osprey Eja,Gregory Maven, and Hyperlite Southwest. But at a minimum, these are 23% more expensive than the $199 Flash 55.

Despite this, I knocked off a half-star because this pack is an incomplete kit. The recommended Medium REI Co-Op Duck’s Back rain cover will set you back another $29.95. You may also need to spend an extra $9.95 for Packmod accessory straps if you’re packing heavy, bulky gear.

REI Co-Op Flash 55 Technical Specifications Chart

The below tables allow you to easily compare every version of the REI Flash 55. Notice that the first table refers to women’s sizes, while the second overviews men’s sizes. 

For insight on how to measure your torso and waist, see REI’s guide on “ How to Size and Fit a Backpack.”

Technical Specs Comparison Chart – REI Co-Op Flash 55 (women’s version)

	REI Co-Op Flash 55 Women’s XS	REI Co-Op Flash 55 Women’s XS Torso, M Hip Belt	REI Co-Op Flash 55 Women’s S	REI Co-Op Flash 55 Women’s M
Load Capacity	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)
Volume	3,234 in3 / 53 L	3,295 in3 / 54 L	3,356 in3 / 55 L	3,478 in3 / 57 L
Dimensions	14 x 27 x 12 in (35.6 x 68.6 x 30.5 cm)	14 x 27 x 12 in (35.6 x 68.6 x 30.5 cm)	14 x 28 x 12 in (35.6 x 71.1 x 30.5 cm)	14 x 29 x 12 inches (35.6 x 73.7 x 30.5 cm)
Fits Torso Length	15-17 in (38.1-43.2 cm)	15-17 in (38.1-43.2 cm)	16-18 in (40.6-45.7 cm)	17-19 in (43.2-48.3 cm)
Fits Waist/Hips	30-38 in (76.2-96.5 cm)	34-44 in (86.4-111.8 cm)	32-40 in (81.3-101.6 cm)	34-44 in (86.4-111.8 cm)
Weight	2.625 lbs (1.191 kg)	2.688 lbs (1.219 kg)	2.688 lbs (1.219 kg)	2.750 lbs (1.247 kg)
Shell A Materials	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop
Shell B Materials	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)
Color Options	Desert Moss, Jasper Green	Desert Moss, Jasper Green	Desert Moss, Jasper Green	Desert Moss, Jasper Green
Price	$199.00	$199.00	$199.00	$199.00

Technical Specs Comparison Chart – REI Co-Op Flash 55 (men’s version)

	REI Co-Op Flash 55 Men’s S	REI Co-Op Flash 55 Men’s M	REI Co-Op Flash 55 Men’s L	REI Co-Op Flash 55 Men’s L Torso, S Hip Belt
Load Capacity	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)	Up to 30 lbs (13.6 kg)
Volume	3,234 in3 / 53 L	3,356 in3 / 55 L	3,478 in3 / 57 L	3,417 in3 / 56 L
Dimensions	14 x 29 x 12 inches (35.6 x 73.7 x 30.5 cm)	14 x 30 x 12 in (35.6 x 76.2 x 30.5 cm)	14 x 31 x 12 in (35.6 x 78.7 x 30.5 cm)	14 x 31 x 12 in (35.6 x 78.7 x 30.5 cm)
Fits Torso Length	17-19 in (43.2-48.3 cm)	18-20 in (45.7-50.8 cm)	19-21 in (48.3-53.3 cm)	19-21 in (48.3-53.3 cm)
Fits Waist/Hips	32-40 in (81.3-101.6 cm)	34-42 in (86.4-106.7 cm)	34-46 in (86.4-116.4 cm)	32-40 in (81.3-101.6 cm)
Weight	2.750 lbs (1.247 kg)	2.813 lbs (1.276 kg)	2.875 lbs (1.304 kg)	2.813 lbs (1.276 kg)
Shell A Materials	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop	100-denier recycled nylon Robic ripstop
Shell B Materials	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)	210-denier recycled nylon Robic (high tenacity yarns)
Color Options	Desert Moss, Jasper Green	Desert Moss, Jasper Green	Desert Moss, Jasper Green	Desert Moss, Jasper Green
Price	$199.00	$199.00	$199.00	$199.00

REI Co-Op Flash 55 Alternatives

Overall, the REI Flash 55 addresses a variety of needs and preferences. However, like any product, there are areas it could improve. If you have concerns about its warranty, water resistance, or other factors, check out these alternatives: 

Hyperlite Mountain Gear Southwest

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I tested the Hyperlite Mountain Gear 3400 Southwest on this same trip — on a day it was dumping snow. While technically water-resistant, its roll-top closure and Dyneema fabric kept all my gear dry. This material is also highly durable and lightweight, with the black 3400 Southwest weighing just 2.2 lbs (0.979 kg). It also grants 64.8 liters of total storage. 

Unlike the REI Flash 55, the Southwest is also available in various capacities. Ultralight enthusiasts will appreciate the 2400, weighing as little as 1.9 lbs (0.872 kg) with 49.8 liters of storage. Or, to carry a heavy load, opt for the 4400. It weighs 2.4 lbs (1.100 kg) and has an impressive 79.8 liters of volume. 

Get more details by reading my Hyperlite Southwest backpack review.

Osprey Eja

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In many ways, the REI Flash 55 and Osprey Eja are similar. They both are available in gender-specific models (the men’s version is the Exos), along with various sizes. A custom-like fit and easy-to-use height adjustment features create unparalleled comfort. They’re also both durable, lightweight, and made with eco-conscious materials. 

However, when it comes to its warranty, Osprey has REI beat. Under its All Mighty Guarantee, Osprey “will repair any damage or defect for any reason free of charge.” It doesn’t matter when or where you purchase your pack, or even who purchased the product. And if you lost that crumpled receipt years ago, no worries.

This high-quality construction means your Osprey pack will likely be around for years. As I share in my Eja backpack review, it”s the kind of investment that may even last a lifetime.

FINAL VERDICT – Is The REI Co-Op Flash 55 Worth It?

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After personally testing this pack, I can confidently say that the REI Co-Op Flash 55 is worth it. Its various sizes and customizable features make the pack highly comfortable. 

It”s user-friendly and great for new backpackers, but also durable for seasoned thru-hikers. The lightweight pack is also water-resistant with its roll-top closure, yet breathable with mesh panels. 

It may not be built for the roughest terrain, nor spacious enough for certain trips. You’ll need to purchase a rain cover separately, and perhaps accessory straps for your tent or bear canister. And, if you were to notice a defect, remediating the situation may require some back and forth.

But, would I purchase the REI Flash 55 again? Absolutely. Overall, my concerns with this pack are minor, and I love that there are easy solutions to a couple of them. For reference, here are links to the accessories mentioned above: 

• Medium REI Co-Op Duck’s Back rain cover, $29.95
• Packmod accessory straps, $9.95

I look forward to backpacking with the REI Flash 55 all through this summer, and for many more seasons to come! 

FAQs About the REI Co-Op Flash 55

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Thanks for reading my REI Co-Op Flash 55 backpack review! I hope you found these insights helpful and enjoy your upcoming backpacking trips. Safe travels!