The Nathan Vapor Air 3. 0 7L Hydration Pack is the next-generation update to this award-winning series. This vest rides high and tight for a snug runner fit with a Contoured Chimney back panel and moisture-wicking air mesh on the back and shoulder straps to keep us cooler and drier as we run hotter and hotter. At the same time, Nathan's Adaptive-Fit Adjustable Sizing System accommodates most body types, including expanded 1XL-3XL sizes. The Vapor Air comes with a 2L bladder and plenty of storage options for our valuables, devices, and snacks.