The ResMed full face cushion is for both the Quattro™ FX Full Face CPAP Mask with Headgear & the Quattro™ FX for Her Full Face Mask with Headgear only. Quattro FX Cushion Features The ResMed Mirage series of CPAP masks have been a wildly popular product with consumers for years, based primarily on comfort. That comfort is derived from the patented dual-wall design. The Dual Wall technology consists of a supportive inner layer that helps stabilize the cushion. That cushion is accompanied by a softer, outer membrane that greatly reduces potential leaks and pressure points. As the air flows through the cushion, the outer membrane slowly and softly inflates around the nose to create a remarkable seal. Both frame and cushion of the Quattro FX are sized. This means that the cushion size must be the same size as the frame to function. These frame sizes and cushions sizes cannot be mixed. Small cushions fit only small masks Medium cushions fit only medium masks Large cushions fit only large masks