In Ear Monitors, Earbuds, Hearing Protection, Earphones, Earplugs
These gel-filled earbuds create a custom fit by instantly molding to your ear shape! - Yanko Design
Custom fit earphones: Audio nirvana or a waste of money? | Ars Technica
Amazon.com: MIPEACE Bluetooth Noise Reduction Headphones, Magnetic Custom- fit Safety Wireless Neckband headphones-29db Noise isolating Work Earbuds Earphones with mic and Control,IPX4 sweatproof 13+Hour Playtime : Electronics