Will salt water harm the Purple® Seat Cushion? Great question! Our Purple® Seat Cushions will not be harmed by fresh or salt water. Related articles Can I cut the Purple™ Seat Cushion to fit a specific seat size? What Purple® Seat cushion is recommend for coccyx pain? How do I clean the Purple® Seat Cushion? Can I leave the Purple material in a hot car? Do you have double mattress?