Pool Central 21 ft. Round Heat Wave Solar Blanket Swimming Pool Cover in Blue

21 ft. Round Heat Wave Solar Blanket Swimming Pool Cover - Blue. Significantly reduces heating costs by up to 80% Superior heat absorption and retention. Reduces evaporation saving water and costly chemicals. Solar blankets are made from a durable polymer material with thousands of tiny sealed air bubbles. They float in. bubble side down in. on the surface of your pool water when the pool is not in use and allow solar energy to pass through which is then trapped as retained heat in the pool.