Sierra Designs Flex Capacitor 25-40L

£112.00 £150.00



Meet the pack that does it all. The Flex Capacitor family of packs feature adjustable volume to handle both short and long hauls, and a Y flex suspension system that carries above their weight class. With three sizes in a 25-40, 40-60, and 60-75 L capacity, there is a flex pack to fit your needs. A bucket lid with a stash pocket closes everything up, while dual stretch pockets on the shoulder straps and side of pack cover all your needs.  The 25-40 Flex Capacitor is the smallest in the range, with enough volume for  fast and light over-nighters or winter day  trips when you need to take extra gear.

What We Think at Valley And Peak

Sierra Designs as per usual has come up with another innovative design in the form of an adjustable volume backpack, meaning you can have a backpack for an overnight or week long trips, simply by adjustment of straps tightening a gusset which cinches the Flex Capacitor down, so everything remains stable on your back.

There is a nice airflow through the gap created by the Shoulders and Lumber pads, to keep you cool during hot weather.

Designed by Andrew Skurka, the well known long distance backpacker. Watch the video above from Andrew to get a good fell for all the features and benefits.    The Flex Capacitor Backpack carries very comfortably even with heavier loads where many packs would feel uncomfortable and unstable .


Read Chris Townsend's review in TGO here



  • Expandable Volume
  • 2 stretch mesh side pockets
  • 2 stretch mesh hydration pockets on shoulders
  • Zippered hip belt pockets
  • U-shaped top access zipper
  • Small stash pocket in lid
  • Ultralight weight
  • Lightweight 'Y' Flex DAC suspension


  • 100D Nylon-Poly Ripstop/420D Nylon Oxford


Tech Specs

  • Capacity: 25-40L 
  • Weight with S/M waist belt: 1100g
  • Weight with M/L waist belt: 1.130g
  • Torso Fit: 16" - 19" / 40.6 - 48.3 cm
  • Hip Fit with S/M waist belt: 29" - 32" / 73.7 - 81.3 cm
  • Hip Fit with M/L waist belt: 32" - 35" / 81.3 - 88.9 cm
  • Dimensions (H x W x D): 23" x 11" x 8.5" / 58.4 x 28 x 21.6 cm
  • Suspension: Y Flex DAC

This product is sourced from our supplier's store in order for us to provide the greatest range offering at the best value prices. Please see our delivery section for more details.