The Sierra Designs Flex Capacitor 40-60 Pack is an innovative, ultralight backpack designed with a focus on versatility, comfort and durability. What sets this pack apart is its unique compression system that adjusts the volume of the pack between 40 and 60 Liters. Take it with you for a weekend or a week-long trip. Simply use the compression straps to keep your load stable and close to your back as your packed weight fluctuates, or you chow through most of your food the first night. The zippered top lid allows for quick and easy in-and-out of the voluminous main compartment. A removable Y-FLEX aluminum frame, and thick EVA foam padded back panel and hip belt make for an efficient and super comfortable suspension system that will surely help keep a smile on your face over long, long distances.