Our top of the line Gorilla winter cover has quality features that are unmatched. The triple strength construction of this cover ensures its long life. The dense thick layer of polyethylene on the top and bottom of the cover are reinforced by a super strong inner scrim that resists rips and tears. The black underside of the cover retards algae growth and heat sealed seams mean a crystal clear pool next spring. Our Gorilla covers have full UV protection embedded in the material to resist the harmful effects of sunlight for many years. The big 4 foot overlap ensures a proper fit and reduces stretching and ripping like covers with 3 foot overlaps."