12 Mil thickness increases surface water temperature up to 15 degrees, extending your pool season enjoyment. Light blue cover color is a happy medium between heat absorption and retention Prevents evaporative heat loss during cool nights Cover cover should only be used when chlorine levels are below 2.5 ppm and pH levels are above 7.2. Using a solar cover reel provides more convenience when removing and applying the cover as well as helping to reduce wear and tear.