No fitting or sizing needed for these pre-molded flanged earplugs. Mack's ® Ear Seals? feature a dual durometer design (2 plastics are used in the molding process). This creates a unique combination of super soft seal rings for unmatched comfort and a stiffer inner core for ease of insertion. Doctor recommended to seal out water, Mack's ® Ear Seals? help prevent swimmer's ear and surfer's ear and come with a convenient removable cord.