Rebound Memory Foam Earphone Tips - Ear Sizing Pack, 5mm Premium heat-activated memory foam softens and shapes itself to your ears. Elastic inner core expands up to 40% to fit and securely grip a wide range of earphone nozzle sizes. Variety of memory foam materials, nozzle sizes, & memory foam sizes to choose from. Comes in a convenient 3" by 4" zippered pouch with spare room for earphones. 60-Day 100% Money-Back Satisfaction Guarantee. If you are not 100% satisfied, return within 60 days for a full refund.