Sunstar Spa Topsâ„˘ Exceed Safety Standards! The Sunstar Spa Topâ„˘ is designed to serve as a thermal insulating locking safety cover for your spa. In 1993, our covers were first tested by an independent lab to comply with the ASTM Safety Standard. All models passed and Sunstar was the first spa cover manufacturer to offer a safety-labeled cover. Then In 1994, Sunstar was the first spa cover manufacturer to receive UL Classification. Our covers are all classified for ASTM Safety on all sizes, densities and models, even swim spas.