ALL SWIRL 21 Ft Round Above Ground Overlap Pool Liner 48" to 52" Side Wall 20 Year Warranty 20 mil 20 Year Manufacturer Warranty Made from 20 mil durable virgin vinyl. Tough, long-lasting 1/2" lap seams. Perma-sealed with state of the art equipment. Contains highest grade UV inhibitors for maximum weather ability and resistance to sunlight, bacteria, fungus, chemicals, and cold crack