This is a water resistant cover that zips around the BioMat, to protect it from sweat, dirt, and oils. It is made with 100% natural materials – cotton and germanium. It is durable and naturally antimicrobial. The BioMat works just as well with or without this germanium cover. However, germanium cover is still a good idea if the BioMat is being used for detox purposes, or as a sauna alternative. Also, this cover is appropriate for professional use cases where sanitation between sessions is necessary.