This cushion comes in four sizes: x-small, small, medium, and large. Make sure you choose a cushion size that will fit your mask and your face.
In the case of ResMed Quattro™ Air masks, the cushion size you purchase needs to be identical to the frame size of the mask. You cannot mix different mask frame sizes with different cushion sizes.
In the case of the ResMed AirFit™ F10 systems, the mask frames come in two sizes. The XS/S size frame will fit either an x-small or small cushion. The M/L frame will fit either a medium or large cushion. You cannot mix large frames with small cushions, nor small frames with large cushions.