Gear Review: REI Flash 45 Backpack

REI Flash 45
$159, 47L/2,868 c.i., 2 lbs. 14 oz. (large)
Sizes: men’s medium (45L/2,746 c.i.) and large, women’s small (45L/2,745 c.i.) and medium (47L/2,868 c.i.)

The challenge: Backpack a three-day, 40-mile loop in Utah’s Dark Canyon Wilderness, staying as light as possible, but having a pack capable of hauling extra water without compressing my spine. It struck me as a good opportunity to test out REI’s latest iteration of the Flash 45 backpack. Having used and reviewed the previous version of the Flash 45, I was curious to hike with this newly updated sack—which has gained about 10 ounces compared to eight years ago (not bad, compared to most people), but also appeared capable of handling more weight comfortably than its predecessor. I discovered that much is true, and that’s among a few improvements to a backpack that’s still under three pounds and, more remarkably, under $150.

The steel, internal perimeter frame with one horizontal stay, plus a contoured hipbelt and shoulder straps with a good amount of breathable, perforated foam padding for a pack this size, carried up to about 30 pounds comfortably, including a gallon of water at times. I’d say the pack’s comfort limit is 25 to 30 pounds; any more weight would overtax the hipbelt. Although the Flash has a breathable, mesh-foam back panel, even in mild temperatures in the 50s to around 60 Fahrenheit, my back got sweaty because the pack hugs you and doesn’t really allow air flow. The shoulder harness adjusts within about a two-inch range.

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REI’s UpLift Compression system employs ratcheting straps extending from near the top of the frame on each side down to dovetailed straps attached to the bottom front of the pack bag. Tightening those straps pulls the pack load upward and inward, not only compressing the load for better stability, but also shifting it somewhat closer to your center of balance (more so when the pack isn’t filled to capacity). I found it beneficial in keeping the pack’s weight more on my hips than on my shoulders, particularly appreciated on the hours-long descents and ascents we had in the Dark Canyon Wilderness, which backpackers face in mountains, too.

REI Flash 45 top compression.
REI Flash 45 top compression.

The top-loading Flash 45 has the capacity for a three- or even four-day trip, provided your gear is light and compact. I fit three days’ worth of food and all of my gear in the main compartment, including a relatively compact, 10° F down sleeping bag and a rainfly. And the extendable, removable lid allows overstuffing the pack for a trip’s first day (although that could make the pack top-heavy and carry less well). A top compression strap helps stabilize an under-sized load or holds an item you couldn’t fit inside, like a jacket or rope.

The pack has a pocket configuration that’s common for this category: six external pockets, including a stretch-mesh front pocket big enough for a rainfly; stretch-mesh side pockets that fit liter bottles and open at an angle conducive to reaching into them easily with the pack on; a zippered lid pocket that held everything I wanted to put in it; and two hipbelt pockets (one zippered, one with overlapping mesh flaps) large enough for a few bars, although the belt’s curved shape means a small camera or phone doesn’t easily slide into those pockets. External attachments hold an ice axe or trekking poles. The safety whistle on the sternum strap is a nice feature. One demerit: There’s only one side compression strap long enough to attach anything bulky, like a foam pad; the UpLift straps don’t have enough length for that.

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REI Flash 45 side.
REI Flash 45 side.

The 420-denier ripstop nylon bottom will withstand much hard use, and the 100-denier ripstop body fabric is adequately durable for normal use; both are not uncommon for packs in this category. And like many similar packs, the mesh side and front pockets are susceptible to tears if you’re not reasonably careful.

What don’t you get at this price? While it’s reasonably stable when hiking on a trail, it still lacks the motion-control design features that you’ll find in a more-expensive pack like the Arc’teryx Bora AR 50. And the Flash 45’s main compartment lacks any quick access such as a panel zipper or sleeping bag compartment zipper—it’s strictly a top-loader.

As REI often does with its brand products, it gave the Flash 45 design features with a proven track record of effectiveness on other backpacks on the market, plus a fairly unique feature—the UpLift Compression system—and sells it at a very competitive price for what you get.

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The Verdict

You can find packs that are more comfortable, feature-rich, minimalist, or capable of hauling more weight. But you will be challenged to find one that compares with the Flash 45 at a better price.

BUY IT NOW You can support my work on this blog by clicking any of these links to purchase a men’s or women’s REI Flash 45 pack at, or a men’s or women’s Flash 55 at

Tell me what you think.

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See my “5 Tips For Buying the Right Backpack” and “Gear Review: The 10 Best Backpacking Packs,” all of my reviews of backpacks and backpacking gear I like, and these stories at The Big Outside:

My Top 10 Favorite Backpacking Trips
10 Tricks For Making Hiking and Backpacking Easier
7 Pro Tips For Avoiding Blisters
The Simple Equation of Ultralight Backpacking: Less Weight = More Fun

NOTE: I reviewed gear for Backpacker Magazine for 20 years. At The Big Outside, I review only what I consider the best outdoor gear and apparel. See categorized menus of all of my gear reviews at The Big Outside.

—Michael Lanza


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