Size:18-ft. Pool The Pool Mate Guardian Above-Ground pool cover protects your pool during harsh winter conditions. This extra heavy-duty polyethylene cover blocks out any dirt & debris throughout the winter. The Guardian cover prevents algae growth by blocking UV rays from entering your pool. Pool owners who use a Pool Mate Guardian pool cover & close their pool with the proper winterizing chemicals will have a clean pool in the spring that will be easy to open. It is always recommended to open your pool by mid to late may. This cover features a 4-foot overlap making it easy to install. Grommets are placed every 4' & should be used with the included cable & winch. Pool owners with larger top rails should consider ordering a larger pool size cover. Ordering a larger size cover & putting the extra material inside the pool can help increase the pool cover’s longevity. This high-quality lightweight cover features heat-sealed seams & is built to last longer. The Pool Mate Guardian Above-Ground pool cover comes with a 12 year warranty.