5 star rating on TrustPilot
Sierra Designs

Flex Capacitor 25-40L


Ex. tax/Non UK:£116.58


The Sierra Designs Flex Capacitor 25-40L Backpack is an Innovative Designed BackPack. The Flex Capacitor Features a Unique Gusset System that Allows the Pack to Quickly and Easily Expand from 25-40 Litres with the Adjustment of a Few Straps. Good for a Fast and Light Overnight, or a Winter Trip Where you Need to Take More Gear.



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.


  • 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

Subscribe to Get a One-time 5% Discount

Plus emails on all sorts of product updates, blogs, tips, tricks, discounts and competitions!

Valley And PeakValley And Peak
Valley and peak

We Manufacture and Supply Ultralight Outdoor Gear. We Manufacture in the UK, Backpacking Quilts, Ultralight Bivys, Groundsheets and a wide range of UL Specialist Accessories.

Made By TapStudio

© 2021 Valley And Peak Limited. All rights reserved.