Heavy-duty polyethylene material works with the sun to catch and retain heat. Helps raise the water temperature by absorbing sunlight during the day and retaining the heat to extend the pool season. Keeps debris out of the pool reducing time spent cleaning. Saving come from a reduction in water evaporation, leading to lowered chemical usage. Material is highly resistant to ultra violet rays which extends product life. Available in standard and custom sizes as well as a wide range of grades.