Plugfones ComforTwist Foam Replacement Plugs feature SoundSeal Noise-Suppressing Technology that acts as a barrier between you and everything you don't want to hear. These interchangeable replacement tips are only compatible with the Plugfones Guardian， Guardian Plus and Liberate 2.0 and have an ANSI-certified Noise Reduction Rating (NRR) of 23 dB when used with those products as directed.