Thermal blankets float on the spa water surface, underneath your hard cover. By using two covers in conjunction with each other, you maximize your spa's heat retention. The hard cover keeps the cold air out and the thermal blanket keeps the heat in the water. It works on the same concept as a double pane window.

Cut the plastic blanket to the same size and shape as the water surface of your hot tub. This blanket is made out of plastic and is filled with thousands of tiny air sacks allowing it to float on the water surface underneath your regular hard cover.

Place the bubble side down in your hot tub.