The Cressi Neoprene Mask Strap Cover is the best solution to help to hold the snorkeling mask on your head. It helps to wear the mask more easily, especially for those with long hair. The hair tends to stick to the silicone and the strap can pull the hair and it's annoying. The Neoprene slips better on the hair, and the large surface adjusts to the shape of the back of the head, holding the mask in place. Won't shift on mask strap: there are Velcro tabs inside the cover to anchor it to your silicone mask strap.