Replacement and only compatible with Mirage Quattro masks, they are not compatible with Quattro FX masks. The Mirage Quattro uses four different frame sizes; therefore the ExtraSmall cushion/clip will only fit the ExtraSmall mask, the Small cushion/clip will only fit the Small mask, the Medium cushion/clip will only fit the Medium mask, and the Large cushion/clip will only fit the Large mask. Dual Cushion The Mirage Quattro features a dual-wall cushion designed for an advanced seal that will conform to the face to help maintain a seal during movement. The cushion also seals at the chin to better accommodate jaw movement during sleep. Spring-Air Technology The Mirage Quattro cushion also features Spring-Air technology which contours to your facial features and helps adjust the mask seal making sure to provide the most secure mask seal you've ever experienced.