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Sierra Designs
Flex Capacitor 40-60L Backpack

4 out of 5 stars
1 Review
Current price: $139.96 Original price: $199.95
30% off

Style & Size:

Size Chart


Flex Capacitor 40-60L Backpack

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

Overall Rating

4 based on 1 ratings

Review Summary

1 Stars - 0 reviews
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4 Stars - 1 reviews
5 Stars - 0 reviews

Fits True To Size

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4 out of 5 stars

February 27, 2021

Great pack!

I've used it once or twice and have initial impressions
Size Bought:
5' 8"

I really like this backpack. It is extremely versatile and handles different types of outings well. I?ve used this backpacking on winter weekend trips and it has handled my heavy winter gear without issue. The compression straps really do an awesome job at dialing in the gear inside while securing my z-seat, trekking poles, and tent stakes on the outside. Being able to attach the mesh bladder pocket to the outside of the pack is a nice feature that I look forward to using in the summer. The hip belt is phenomenal with lots of room for adjustments. I do have two suggestions for the third generation that would make this a 5 star pack. 1. The lid?s pocket needs to be bigger. There is a lot of real estate there for a larger pocket that goes unused. This was a complaint of the original version so it?s disappointing to see that it wasn?t addressed. 2. The side pockets could be improved. They hug the pack so tightly that I find it difficult to fit a smart water bottle in them with the pack off. This will be more of an issue in the summer months when I drink more water and won?t want to constantly be refilling the 16 oz bottles that fit in the should strap pouches.