Our Grand 12 Solar Covers are our standard solar pool cover. Its made of a tough 12 mil material and is covered by a 5 year warranty. This is a one piece cover that will stand up the harshest sun, and the coldest cold. These solar covers are make of durable resin and have thousands of little air bubbles that will transmit and capture the sun which will generate solar heat to your pool. Being thicker, it will help hold in the heat at night better than the 8 mil. This process will result in an average temperature raise in 15 degrees.