For record-breaking car-to-car travel times, we pack everything you need into the Mammut Aenergy 18L Daypack. Running vest style shoulder straps have 2 pockets to store soft water bottles for convenient hydration that won't slow us down and the lightly padded back panel makes it comfortable to carry without weighing you down. As the trail gets steeper and our pace quickens the strap on the sternum of the bungee stretches with our breathing allowing our lungs to expand freely. In addition to the design speed-oriented this backpack has a partially redesigned design which reduces carbon dioxide emissions.