ProView – Sierra Designs Flex Lumbar 3-6

I am a long time lover of the fanny pack. In my humble opinion, they never went out of style. When I started seeing them in Instagram ads and magazines over the past few years, I was overjoyed. Finally, I could wear my long time loved fanny packs in style. You bet I still have a corduroy fanny perfect for trapper keeper odds and ends, scented erasers, and keychains. Was this the perfect accessory for a night on the town? Absolutely. Could it accompany me on a mountain bike ride. Absolutely not. When I saw Sierra Designs had taken their Flex Capacitor design and shrunk it to 3-6 liters, I knew it would be the perfect hiking and biking companion. 

Sierra Designs Flex Lumbar 3-6

Product Description: The Flex Lumbar collection takes the same expanding gusset found in our Flex Capacitor, and shifts it vertically to work as a lumbar pack. Integrated water bottle pockets and enough room to stash a layer and some food means you have your bases covered for any day hike. Flex it open when you need to carry more, or cinch it down when you want a lower profile pack.

Offer price: MSRP: $49.95

  • Comfort
  • Versatility
  • Fit
  • Weight


I would highly recommend this pack for anyone who likes to move quickly and unencumbered in nature. The flexibility in size, and the stability from multiple cinch points, make it a great companion that you can almost forget about until you need a refreshing drink or an extra layer. 



  • Able to carry many different things, big and small
  • Multiple cinch points
  • Stable


  • Zipper length is too short to fit larger items
  • Water bottle holders can be unstable with large bottles

With the world flipping upside down, I put all my effort into exploring my backyard. This included hiking and biking odd trails and finding dead ends. I would have no idea how far I was going to go, or how long it would take. The Flex Lumbar 3-6 was the perfect companion for these excursions. I have researched deep into the posture and functional movement world, and backpacks aren’t your best friend. This lumbar pack allowed me to bring food, water, bike tools, and an extra layer, and not put weight on my shoulders.


This is where this lumbar pack shined. At eight ounces, you are already starting out super light. Once I had loaded the pack down, it still sat nicely on my hips and snug once I pulled both tabs. I appreciated the two tab holders so the straps never flapped around. I would have liked to see the two nylon straps tighten from the sides closer to the fanny pack, instead of the clasp, to get a more precise fitting. I also found that if I loaded the pack down with water on a hike, it would slide a bit down my hips into a less comfortable position. I rarely had that much water with me, so I didn’t see this as a huge issue.

The lumbar pack really is comfortable. When I have weight on my shoulders from a pack, I tent to pull my shoulders forward and hunch, both while I’m walking and when on a bike. Keeping the weight all in my hips allowed me to work on correct form in both sports. It also kept my back free of the classic sweat drench.


We all know how I feel about fanny packs, so really I’m going to be happy with the style no matter what. That said, I appreciate that the style adds to the function. The zipper pulls have yellow nylon pulls, and closures have opposing colors so you know exactly where to pull. This makes tightening straps and securing items quick and easy.


There are a few features that I especially enjoyed in this lumbar pack. The first being the ‘secret’ pocket behind the large one. It’s hidden away and a little tucked, but it’s PERFECT for a cell phone. This was my designated cell phone spot every time I wore it. I never had to dig around in the main compartment, around my jacket, keys, and snacks, to pull out my phone. I wish I didn’t use my phone as much as I do on walks, hikes, and bikes, but the accessibility made it less annoying. 

The expandability from three liters to six is super helpful, making this pack versatile for many sports. The three compression straps along the pack allow you to adjust the pack to the exact size you need, without any extra room. It also allowed me to pack it up, then tug down on the straps and cinch everything together. This was especially helpful when I was mountain biking and needed the pack secure on my back. 

There are water containers on either side, with elastics to hold those bottles in. I found smaller bottles worked best, or, if I only had one, I put it directly in the large compartment. This kept the water super secure, and the pack balanced. There are also cinch points that go from lumbar pack, to hip strap. There were helpful to secure a water bottle if I was using one, or, compress the pack so it was closer to my body. There is also a smaller mesh pocket right next to the water bottle holders. This is the snack/gummy pocket. It kept snacks super accessible, but also secure when I was cruising down single track. 

Pro Tip: The water bottle holders can double as poop bag holders, for both empty and full bags. Yes — gross. But what’s grosser? I’ll tell you — leaving your dogs droppings the side of the trail. 


Here are the exact specs from Sierra Designs: 
Capacity: 3-6 liters / 183-366 in3
Weight: 8 oz / .23 kg
Hip fit: 52″ / 132 cm max
Dimensions (H x W x D): 6″ x 10″ x 5″ / 15.2 x 25.4 x 12.7 cm

This pack is incredibly “packable.” My only issues occurred when trying to stuff hard sided objects through the zipper enclosure. The pack can get plenty big, but items you put in it must be malleable, or smaller size. 

At it’s most I carried:
1 liter of water
Rain jacket
Cell phone
Bike tool

At it’s least I carried:
Roll of dog bags
Cell phone

Both times were comfortable. It’s nice to know it can be loaded or unloaded and still be easy to wear. At one point I only brought my GH5 Lumix (DSLR) camera with me. I was pleased that it slide easily into the pack and zipped shut. 


So far I have had no issues with durability. The 100D Nylon-Poly Ripstop material feels durable and not prone to holes. I think this will hold up longer than a backpack because I’m never putting it on the ground. Usually, with a pack, every time I break, I take off my backpack and give my shoulder a rest. This lumbar pack stays on the whole journey, and therefore never touches the ground.

The Flex Lumbar pack was perfect for the uses I needed it for. I took it hiking and mountain biking often. I plan on using it this summer for fly fishing, and in the winter while I cross country ski. It also addresses the age old issue of women’s clothing never having pockets. Finally I can keep all my items on me without the need of a backpack or jacket with pockets.

The Final Word

Overall, I really enjoy using this pack. The only issues I’ve run into is the water holder feeling unstable when loaded down with big bottles, and the zipper for the main pocket being a little small to fit larger items into the pack. Otherwise, I really enjoy letting my back breath and my hips take the weight of the few things I always want with me. 

I would highly recommend this pack for anyone who likes to move quickly and unencumbered in nature. The flexibility in size, and the stability from multiple cinch points, make it a great companion that you can almost forget about until you need a refreshing drink or an extra layer. 

Find Sierra Designs on Outdoor Prolink. Not a member? Apply today!

About the Gear Tester

Outdoor Prolink Pro
Roxy Dawson
Content Marketer :: Outdoor Prolink | Website

Roxy Dawson lives in a van full time and travels around the country working as an adventure journalist, searching for backcountry adventure, and using her dog as a pillow. Like most adventurers, she loves coffee, hot springs, and getting pretend lost. She works for Outdoor Prolink as the Content Marketer. She is trying to make a small positive impact on the world, and a larger one in her community. Follow her on Instagram at @roxyjan_

One comment

  1. Outdoor Prolink Pro

    Everyone loves a hip pack!


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