The Dakine 3L Hydrapak design of the Replacement Reservoir is engineered to be durable and easy to use. The Shape-Loc center baffle adds some rigidity to the shape of the bladder, which cuts down on shifting of water weight while you're in motion and makes for a more resilient design. Meanwhile, the wide-mouth opening and plug-and-play connecters make it easy to fill, drain, and clean. And, of course, it's BPA- and PVC-free.