The source whistler 20l hydration pack the whistler is our ultimate freeride hydration backpack designed by pro riders for source it holds up to 3l of hydration and 20l of cargo and it features a rain cover helmet sling and many other practical features to store protectors and any other gear needed on the trail source whistler 20l hydration pack features lightweight fabrics ripstop 70d nylon loop for helmet attachment padded shoulder straps valve docking station adjus