Arctic Armor covers are woven strong/long-lasting polyethylene tapes to produce a cover that will hold up to winters worst. Arctic Armor covers are constructed of an extremely tight weave fabric that does not allow light to pass through. Without sunlight, algae cannot grow! Arctic Armor use an extra foot of material—another reason why they are a great value! A 4-ft. overlap on above-ground pools provides a better fit, especially on pools with extra wide top-rails. This extra fabric also takes up some of the slack during windy weather, helping to prevent excessive wear and tear.