In-Ground Magni-Clear Solar Blanket 14-mil -20' x 40' Rect.: Pool Solar Blankets. Tip says, "Get the Magni-Clear. It's thicker and let's in more light. Make sure it's rectangle and not round. I got the largest I could.You also have to think ahead to spring when you take it off and store it. It was easier to store 3 instead of one giant one and not as heavy. Also I think it's best to store out of the sun and in a cool place to keep the plastic from breaking down too soon."