In The Swim 12 Mil Blue/Black 21 ft Round Swimming Pool Solar Blanket Cover 12-mil thick solar blanket constructed from poly-resin Thousands of tiny air bubbles work to transfer solar heat into your pool Reduces chemical loss through evaporation, saving time and money on chemicals and rebalancing Can be easily cut or trimmed to fit kidney, oval or irregularly shaped pools Backed by a 7-Year Limited Manufacturer's Warranty