The Dakine "Hydrapak" Vertical Hydration Pack Reservoir is a replacement reservoir engineered to be durable and easy to use. The Shape-Loc center baffle adds 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. While the wide mouth opening and plug-and-play connectors make it easy to fill, drain, and clean. And, of course, it's BPA and PVC free.