Sierra Designs Flex Capacitor is the first 40-to-60-liter expandable backpack

Hikers are notorious for owning a multitude of differently sized backpacks that suit the varying lengths, conditions, and distances of individual outdoor excursions. Sierra Designs Flex Capacitor sets a new standard, making for a two-in-one package — a single backpack that can transform from a 40- to 60-liter volume almost instantly. 

The pack is designed to serve as a versatile solution for hikers and backpackers without sacrificing weight or durability, in addition to contributing a few innovative luxuries of its own. The Flex Capacitor’s frame is constructed of lightweight aluminum with enough rigidity to ensure complete support when loaded to capacity. Weighing in at 2.5 pounds when empty, the backpack is comparable in weight to other packs in the 40L class and boasts a lighter position on the scale alongside other 60L packs.

The volume transformation design is simple, utilizing multiple reach-around cross-straps that tighten or loosen according to load size. Importantly, the pack expands outward, rather than upward or downward. The ability to transition between two drastic sizes while remaining carrier-friendly is unprecedented in the world of backpacking gear. Features to ensure comfort include the unique “Y-Flex” suspension design, EVA foam-filled hip belt, shoulder straps, lumbar, and scapula pads, as well as an adjustable hip belt with its own respective stabilizer straps.

The popular outdoor gear company Sierra Designs did not halt its aspirations with adaptability — instead, it engineered a functional pack equipped with plentiful bells and whistles as well.

The Flex Capacitor features a zippered stash pocket on the lid, a removable reservoir sleeve, two hip belt pockets, and compression straps. In addition, the backpack provides a loop for either ice axes or trekking poles as well as an exclusive shoulder strap water bottle pocket.

The Flex Capacitor is offered in two different torso sizes and four different hip belt sizes, retailing for $200 on the Sierra Designs website.