These are the floating rings that harness the power of sunlight to raise the temperature of an average-sized pool by 3° - 4° F per week. They require less effort to maneuver and store than traditional tarp covers, and eliminate the need for energy-consuming electrical heaters when covering just 70% of the pool's surface. Rated at 21,000 BTUs, each ring also acts as a partial barrier, helping to slow evaporation of water and chemicals, in addition to reducing heat loss at night. Connected by low-strength magnets, the rings separate quickly and easily, eliminating tangles that can occur with traditional covers should anything fall in. Each ring inflates easily without the need for a pump. Imported UV-resistant poly-vinyl. Set of two. 1" H x 60" Diam. (2 1/4 lbs.)