THIS IS A SIZE MEDIUM REF# 63551 This is the replacement Nasal Cushion for ResMed AirFit N20 and N20 for her Nasal CPAP Masks. InfinitySeal Cushion: The N20’s innovative silicone cushion is designed to fit everyone while accommodating movement during the night. The cushion is constructed with varying thickness to unsure a stable fit. The design features a top section having a softer area to stay on the nose bridge while the middle section has increased supportive side padding. A flexible under-cushion insures a good seal and the bottom cushion is contoured with a soft lip envelope.