Bloccs have been designed to easily stretch over and cover a cast or dressing. To be watertight the protector needs to completely cover the cast or dressing, and a comfortable skin-tight seal should form around the arm. Bloccs arm covers are available in MULTIPLE SIZES. Finding the right size cover is very important to ensure a good fit and a watertight seal, you'll need to select a product long enough to cover the cast (extra length is okay) that is comfortably within the arm circumference range. Consider adult and child sizes when measuring. By ordering TWO Bloccs covers, you can have a cover for showering and another for the pool! Bloccs make a great gift! Why not send a cover to a loved one you are wanting to help with their recovery?