Swimline 30' ft Round Swimming Pool Winter Cover + 3) 4x4 Air Closing Pillows Pillow Size: 4'x4' Pillows are used to push your pool cover up off the water's surface so the water won't freeze to your pool cover Pillows are used to keep water off the top of your pool cover Pool Size: Fits 30' Round Pools U.V. Inhibitors Protect the Cover From Sun Damage