BMH Spa Foam Floating Cover - Light Grey or Sky BlueBMH 20 mm spa foam covers keep the heat in, particularly during winter, saving energy and money while keeping your hot tub clean when its not in use. Not all foam spa pool covers are alike, and there can be critical differences in performance. Made from lightweight yet durable 20 mm closed cell polyethylene foam, BMH spa foam covers are designed to deliver years of trouble free use. They sit directly on the water surface, reducing heat loss where it