Premium 18′ Round Blue Solar Cover, 12 Mil

12 Mil Blue Solar Blanket Warms Your Pool for Free. Put the round 12 mil blue solar blanket on your 18 ft pool to heat your pool water by up to 15 degrees using nothing more than the sun’s rays. Thousands of tiny air pockets and an aluminized layer on the bottom of the solar blanket transfers the energy as heat into the water.