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Sierra Designs Flex Lumbar Fanny Pack Review

Looking for a hip pack that’s lightweight, comfortable, and works well for shorter rides? The Sierra Designs Flex Lumbar might be the fanny pack for you!

Although it appears to be designed primarily for hiking, I found it to be a great choice for 1-2 hour mountain bike rides, and road bikes of any length. Thanks to it’s expandable design, it manages to fit a jacket as well as ride essentials (pump, multi-tool, etc).

Of note, it doesn’t have a hydration reservoir, so if that’s something you’re after, look elsewhere. It does, however, have 2 water bottle holders.

sierra designs fanny pack

Review In A Nutshell


  • Size-adjustable–grows from 3L to 6L thanks to cinch straps
  • Lightweight and comfortable
  • Perfect size for short-ish rides, holds more than a jersey pocket
  • Well-constructed and durable, easy-to-clean Ripstop fabric


  • Back and hip panels aren’t that breathable

Price & Where To Buy:

sierra designs flex lumbar review

Sierra Designs Flex Lumbar Video Review

Utilizes Two Water Bottle Holders Rather Than a Water Reservoir

Unlike most of the hip packs we review on this site, the Sierra Designs Flex Lumbar does NOT come with a hydration reservoir. Instead, it offers two mesh pockets for storing water bottles.

This may be a plus for women who don’t love the hip packs with water reservoirs. The hoses on those packs tend to come unfastened and are often a little too long for slim female waists.

I found that the water bottle pockets work well, and I didn’t have issues with water bottles falling out even on bouncy sections of trail. That said, I wasn’t able to figure out how to take the bottle out of the pack while on the bike, so ended up preferring to ride with my bottles in frame-mounted cages instead.

So Lightweight and Comfortable You Might Forget You’re Wearing It

The one thing about the Flex Lumbar pack that really won me over is how lightweight and comfortable it is. In all seriousness, it was easy to forget that I was wearing it at all (especially when I was using it only for gear and not for water).

Unlike some hip packs that dig-in to your tummy or hips, I found that the Flex Lumbar didn’t punch or rub. Of course, this is largely due to the fact that it’s relatively small and I wasn’t using it to carry too much water.

Buckle and waistband straps

There are elastic straps to help secure excess waste band. I appreciated this as a smaller-waisted woman. On my Osprey Seral, I have to use hair bands to secure the excess strap, and as I’m sure you can imagine, that looks a little dorky.

Works Well For Short-ish Rides Where You Still Need To Carry Gear

The pack quickly became my go-to for 1-2 hour trail rides. It has enough space for the essentials–tools and a jacket–and provides easier storage than a jersey pocket.

using the sierra designs flex lumbar for mountain biking

I found that I also really liked using the Flex Lumbar for road riding. I always get stressed about figuring out how to stuff everything I need in a jersey pocket, especially when riding in cooler weather where I may need to strip layers.

The Flex Lumbar is small, unobtrusive, and let’s you bring along the essentials.

Two Zippered Pockets

The pack has two zippered pockets, one at the front and one at the rear of the pack. The larger front zippered area includes two interior open pockets and a clip for your car keys.

Key clip (left), rear zippered pocket (center), and front zippered pocket (right).

The smaller rear pocket is simply a large open pocket but works well for carrying my cell phone and keeps it from getting scratched by tools in the larger pocket.

Finally, there are two small mesh pockets on the hips. These aren’t zippered, so I wouldn’t put anything too valuable in them, but they are ideal for easy access to gels or other small snacks.

hip pocket
Mesh pocket on the hip

Of note, there is no external storage on the pack for carrying protective pads or other gear. If you are using the hip pack solely for mountain biking, you might want to choose a pack like the Dakine Hot Laps instead–which does have external lash straps for protective gear.

Expands From 3L To 6L Of Storage Space

How much you can fit in the front pocket is determinate on how far the front straps are cinched down. At it’s smallest, the pack offers 3L of storage space. If you open the straps all the way, you expand your storage space to 6L.

For me, this equated to enough room for a rainjacket, car keys, a mini pump, tire levers, a multi-tool, an energy bar, and my phone. After I put my rainjacket on, I could cinch the size of the pack back down so it’s not as bulky.

flex lumbar easy access
The pack is easy to swing around for quick access to snacks or other gear.

The pack also comes in a bigger size (7-10L) but it seems this would be better suited to hikers than to bikers. Like the 3-6L version reviewed here, the bigger size does not have a hydration reservoir either.

Back and Hip Panels Are Comfortable But Offer Limited Breathability

The panels where the pack lays against your back and hips are padded but lack the breathability of other packs we’ve reviewed. There is a bit of indentation in the foam to allow for airflow, but it’s pretty minimal.

The back panel on the Sierra Designs Flex Lumbar (left) doesn’t have as much breathability as the Dakine Hot Laps (right).

I didn’t have any issue with my back getting sweaty during testing, but I’ve been riding in near-freezing October weather. I do think the pack might get a little sweaty if riding in sweltering summer temps.

Well-Constructed and Durable

Everything on the Sierra Designs Flex Lumbar pack seems to be well-constructed and durable, as one would expect from Sierra Designs. The fabric is ripstop and easy to clean. I’ve been on a few wet, muddy rides with the pack and it wiped down easily with a wet rag.

Good For Multi-Sport Applications

If you want a pack that will work for hiking or trail running in addition to biking, the Flex Lumbar is a good choice for that. I took it out for a trail run and found that it was comfortable and didn’t flop around like a traditional hydration pack would.

Carrying Loop

The hip pack has a loop for hanging storage at home, or for carrying it when off the bike. It’s bigger than the straps on some of the other hip packs we’ve tested which we appreciated and made it easier to actually use.

carrying strap

Bottom-Line: A Lightweight, Comfortable Pack That Works Well For Short-ish Rides

If you are looking for a hip pack that works well for 1-2 hour rides, or even for use on a road bike, you’ll like the Sierra Designs Flex Lumbar. It holds a spare layer and basic ride essentials but manages to be super lightweight and comfortable. It does not come with a hydration reservoir, which may be a pro or a con depending on your personal preferences.

Disclosure: We were not provided with any monetary compensation to write this review and all opinions are our own. We did, however, receive a pack from Sierra Designs to help facilitate the review, and are an affiliate of Sierra Designs.

Other Pack Options

Want to do some more research before buying? Here are more options and reviews for you.

About The Reviewer

kristen bonkoski

Kristen Bonkoski is the founder and owner of Femme Cyclist.

An avid cyclist for a few decades now, she took to cycling during her late teen years — a time when she needed something to help boost her self-esteem and confidence.

Mission accomplished, the sport has become an important part of her life.  Kristen’s favorite disciplines are mountain biking and bike commuting, although you can also find her cranking out a century on her road bike and touring with her husband and son.  If it has to do with two wheels, she enjoys doing it.

Kristen is a certified USA Cycling coach, and she runs Rascal Rides, a website about biking with kids.

IG: @kristenlbonkoski

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