Spa Slip is a cosmetic upgrade for your likely beaten and ugly hot tub cover. It is geared towards more protection of your insulating hard cover. The Spa Slip is custom fit to cover your expensive hard cover. It is made of a polyester, weft inserted, knit laminate. It is mildew resistant and fade resistant. This is a great product for winterizing your hot tub, adding protection and postponing the eventual failure of your expensive hard cover.