When we first introduced our patent pending Flex Capacitor in 2016, it became an instant hit with the backpacking crowd, and has continued to be a favorite choice ever since. We set out to design a backpack that was as flexible as your adventure could be – suitable for both quick trips and longer stays in the backcountry – and the end result was everything we hoped it would be and more. Now entering its fourth year in our line-up, we decided it was time to reintroduce you to this Sierra Designs modern classic.

Key Features:

Adjustable Volume: The Flex Capacitor features a lateral expandable gusset system which allows it to expand from a volume of 40L to 60L. This means that as the day goes on and layers come off, or you’re done with the trip and the campsite needs packing out, everything is easily stored in your pack with the simple adjustment of a strap or two. There are also two larger compression straps which go around the entire outer circumference of the bag, allowing you to not only decrease the volume even further, but also secure accessories like trekking poles or shovels to the exterior of the pack.

Y-FLEX Full Suspension: This internal, stiff vertical frame has just enough torsional flex to remain comfortable while still supporting all of the gear on your back. When you have to pack everything up and the weight starts to climb, this frame also helps stave off lower back and shoulder pain by evenly distributing the load across the entire pack. The Y-FLEX system also allows for….

Back Panel Airflow: With a simple back panel made of one larger lumbar pad and two shoulder (or scapula) pads, we were able to free up the area between to allow for amazing ventilation between the pack and your skin. This is especially helpful on those hot summer hikes. Normally in order to achieve this feat, you would need to overbuild in other areas to compensate, but the Flex Capacitor avoids this trade-off while still keeping the total weight around 2.5lbs.

Six Exterior Pockets + Easy Access Zip Top Lid: That’s right. There are six, generous, easily accessible pockets that allow you to pack away all of the little things that make your stay in the backcountry a little bit nicer. Plus, the zip top lid allows you to quickly and easily access your gear without having to deal with buckles, pulleys, or roll-tops.

It’s true, there are a seemingly endless number of choices out there for packs – but few can boast all of the features of the Flex Capacitor for the price and weight – and let’s not forget style. It’s one of our bestsellers for a reason, and if we absolutely had to choose a favorite piece of gear in our line, this one would be in the top 5 (come on… you don’t really expect us to choose just one).

Already have one? Send us pics of it out in the wild, or leave a review! There is nothing we love more than hearing your stories. Decided after reading this blog that you need one? Shop away!