Space Age swimming pool solar cover is made of heavy-duty polyethylene material works with the sun to catch and retain heat. Savings come from a reduction in water evaporation. Material is highly resistant to ultraviolet rays which inhibits deterioration. A test conducted by a leading test laboratory shows 14.6% greater heat retention than conventional covers. 8 mil covers has a 5-Year & 12 mil covers has a 10-Year Warranty.