GLI Pool Products 20-1836RE-MSM-GRY-AC 18' x 36' Gray Max Shade Mesh Safety Cover. GLI safety covers are constructed with heavy duty polypropylene webbing and UV treated polyester thread to create the strongest safety covers in the marketplace. A GLI Safety Cover is a safe solution for any homeowner. Not only will your backyard look great, but installation is easy and the “Peace of Mind” that you will carry throughout the winter months is well worth the investment.