The Sierra Designs Flex Capacitor is a top-loading backpack with a unique top lid and two side water bottle pockets. Designed by Andrew Skurka, it has wrap-around compression straps that let you shrink or expand its capacity from 40L to 60L so you can fit more food and gear inside when you go on longer trips. This is complemented by a stiff but lightweight frame that makes it possible to haul heavy loads, far exceeding those that can be carried by similarly sized ultralight or internal frame backpacks.

This is the second generation of the Flex Capacitor, released in 2017.  A third generation was released in ~2019 or 2020.

See picture of tag for full specs (M/L size, M/L hip belt), here here are a few:

-Torso range: 18-21 inches (M/L)

-Hip Belt: 32-35″ (M/L)

-Weight: 2lbs 11oz

-Volume: 40 – 60L (expandable)

-Weight capacity:  50+ lbs

Condition:  I bought this on Geartrade as a new (with tags) pack from a private party.  It looked new, but there were two small abrasion spots in the back fabric, inside the pack in front of the hip belt… someone had obviously carried something heavy with hard corners.  They weren’t a structural or integrity concern to me, so I covered them with gear tape (black patches in pic looking inside pack) and kept the pack.

I’ve used the pack for a few overnight trips, and found it comfortable for me at <25 pounds, but above that (when I added a day’s worth of water), it wasn’t very comfortable for my 60 year old back with a degenerated disc.

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