This 5 pack of Swimline 10 Foot Double Water Tubes is made specifically for use with your rectangular or oval pool cover to eliminate stress on your pool and the cover. It’s 33% heavier then other water bags, making it super durable, and its valves are easy to fill up with a garden hose. This Swimline water tube is best used with in ground pool covers. Covering your pool with a winter cover keeps out dirt and debris. Keep the your winter pool cover in place with the Swimline 10 Foot Double Water Tubes.