Well designed product, this is my second from the Etymotic line of earphones. Sound isolation is key. Snug fit in ear canal provides excellent sound isolation, better than my active-noise-cancelling Bose headsets on flights. Was able to have my MP3 device on lowest sound setting even while in flight. HOWEVER, DO NOT WEAR THIS WHILE PLANE IS ASCENDING OR DESCENDING, as changes in cabin pressure can cause damage to your ear, due to the snug fit in the ear canal. This showed the fit creates an air chamber between ear plug and your tympanic membrane. This air chamber in some ways impede the low frequency response, since tympanic membrane movement is required to perceive low frequency response. Do not therefore expect the boomy bass response like other headphones or earphones.