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Sierra Designs Flex Capacitor 40-60L Backpack


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  • Birch, S/M Bag / S/M Hip Belt
  • Birch, S/M Bag / M/L Hip Belt

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Great Scott!

No, you might not be able to travel through time using this pack, but there's a good chance it's a gift from the future. The Sierra Designs Flex Capacitor Backpack can expand and compress throughout your trip as your needs change, and it does so with lightweight stability. A unique gusset system on the back lets you enlarge the bag to 60 liters at the start of your trip, then tighten it down to 40 liters as your food reserves dwindle and you've moved layers from bag to body.

Whether your trip last two days or seven, you'll be glad for all the places to stash your stuff, thanks to seven different pockets as well as loops on the back for your ice axe. If you're trekking through uneven terrain or might encounter snow, the compression straps can help keep the necessary tools attached, waiting and ready for deployment. A zippered stash on the top of the bag is a perfect hiding place for the vitals you'll need throughout the day, and there's even a spot for your reservoir should you get thirsty.

  • Versatile pack for short and not so short adventures into the wild
  • Can expand in capacity as you pack and unpack throughout the trip
  • Durable ripstop construction fends of sharp rocks and branches
  • Y-Flex internal suspension provides torsional load bearing support
  • Raised lumbar and scapula pads provide comfort and air flow
  • Compression straps can secure snow shovels and trekking poles
  • Mesh pocket on shoulder strap for easily accessible water bottle
  • Item #SDS009G

[body] 100D Nylon-Poly Ripstop, [bottom] 420D Nylon Oxford
40 - 60L (2441 - 3661cu in)
Y-Flex (DAC pressfit aluminum)
Shoulder Straps
yes, padded
Waist Belt
yes, padded
Hydration Compatible
top, U-shaped zipper
2 zippered waist belt, 1 zippered top lid, 2 side stretch mesh, 1 strap bottle
Ice Axe Carry
Trekking Pole Carry
Weight Capacity
35 - 50lb
30 x 13 x 10in
Claimed Weight
2lb 11.2oz
Recommended Use
Manufacturer Warranty

Tech Specs

What do you think about this product?


>Rating: 5

Very happy with my Flex Capacitor

I've used it several times

I purchased my Sierra Designs Flex Capacitor backpack from Backcountry prior to embarking on a 6 day hike of the famous 'Overland Track' in Tasmania, Australia. I was very happy at the performance of the backpack. It stabilised the load very well with the compression straps, and was comfortable and firm to wear. At the end of each day, my back was not sore. It was easy to access with the zip. I liked being able to compress it in further as I ate my way through my food over the hike. I highly recommend this backpack. I love that it works well for weekender getaway hikes as well as multi-day hikes. In fact this backpack will virtually every trip, due to its capacity to expand from 40L - 60L. It's also very light for the load capacity it will handle. No regrets. Recommended.

>Rating: 4

Hip Belt Sizing Help

I gave it as a gift but have feedback to share

>Rating: 5

Does It All

I've put it through the wringer

I love that this pack can do pretty much anything. I mainly do quick weekend trips but wanted to have a pack that can do the occasional longer backpacking trip. This is such a simple pack that it has even worked well for travel.

>Rating: 5

Super Innovative Pack!

I've used it several times

The innovation in this pack is truly incredible. I love that it can expand between 40L-60L, which makes it super versatile. No need to have a weekend pack and a separate pack for weekend+ adventures. The Flex Capacitor can meet the demands of both without really adding weight. Nice work Sierra Designs!


Admiring the view!


How to fit the Flex Capacitor


Flex Capacitor review w/ Andrew Skurka

Check out this great video with Andrew Skurka discussing the thoughts and details behind the Flex Capacitor 40/60 pack.


What are the hip belt sizes for each pack?


What size waist belt do these packs ship with? I know there are four different sizes. Thanks in advance!