Swimline Boulder Swirl 18ft. Round Overlap Above Ground Pool Liner is made with only the finest quality materials used during manufacturing. The liner base is made from 100% virgin vinyl that have algae and UV inhibitors. A proprietary Lamiclear acrylic top coat is layered on the vinyl base to offer protection against pool chemicals, abrasions and UV fading. Lastly, both these layers are sealed together using lap-welded seams for a flawless finish.