Thanks for your review. The Bose QuietComfort Ultra Earbuds utilize both passive and active noise reduction technologies. Passive noise reduction is similar to when you wear earplugs; there is a physical blockage preventing some sound from entering your ear. This is achieved through the earbud design with materials such as silicone eartips, and the acoustic seal created by having a proper fit. For active noise cancellation, your earbuds use sophisticated proprietary electronics with microphones both inside and outside the earbuds. The electronics system senses the sound in almost any environment and then measures, compares and reacts – instant by instant – to produce an opposing cancellation signal.

-Jolie {Bose Customer Support}