This ultra-lightweight hydration pack is ready for anything, from a recreational weekend trail run to the most aggressive ultra-marathons. Because Nathan tests all their products on professional runners, you know this pack has been approved by some of the best athletes around. The Air not only packs a 2-liter hydration bladder, but also has two front bottle pockets, a mesh pocket that holds several gels, an easy-clean pocket to hold empty gel packs, 4 rear gear attachment points, water resistant pill pocket, smart phone compatible pocket and an additional 5-liters of storage not counting the bladder. If you’re thinking this sounds like a bulky day-hike pack, think again. The Vapor Air weighs only 9.3 ounces with the bladder.