The high-density thermal-resistant foam provides extra insulation and minimizes heat loss. Thus the spa stays hot easier with only half the energy use and half the energy cost. The cover also keeps dirt like leaves and vermin from entering into the water. It also protects the spa from punctures, scratches, and weather damage. The cover can be easily attached to the spa and will not be blown away from it so all the heat remains well in the bath. vidaXL