ResMed AirFit™ N30i replacement cushion is the silicone seal that attaches to the nasal style CPAP mask. Facial oil build up on the silicone will break down the consistency of the cushion over time and lead to mask leak. When this occurs it is time to replace your AirFit™ N30i seal. The cushion seals are color coded to easily recognize the size you need to replace. The small cushion has a red dot while the medium is blue, small-wide is purple and wide is gray.