Keep water and heat in and debris, leaves, and trash out of your pool with this Flowclear Solar Pool Cover. Above ground swimming solar pool covers create a greenhouse effect in your pool. Solar covers also prevent water evaporation caused by dry winds, or free-chlorine loss caused by UV rays. , , These covers are designed to keep water and heat in, but debris out. Extend your swimming season with a Flowclear Solar Pool Cover. It fits 18'/5.49m diameter Fast Set pools