The Salomon Agile2 2 Set Pack is so lightweight and low profile that it's almost unfair to call it a backpack. It has a an ergonomic, non intrusive design that you'll hardly even notice while you're running. The included 1. 5L bladder holds enough water for long runs, and the zippered main compartment offers room to store an extra layer. It also has a small stretch pocket on the shoulder strap for energy gels or small snacks so you can stay fueled without having to stop. A breathable back panel and mesh straps help you stay cool and dry whether you're hitting the asphalt or the trail.