The ResMed AirFit F40 is the smallest full face mask ResMed makes, and it wears like it. Instead of stretching over the bridge of your nose, the AdaptiSeal silicone cushion seals just under your nostrils and over your mouth, so you keep a clear line of sight for reading, wearing glasses, or watching TV before you fall asleep.We recommend it if you sleep on your side, breathe through your mouth some nights, or have felt boxed in by a bulkier full face mask before. The frame is a single flexible piece that moves with your face instead of fighting it, and the headgear clips on with magnets you can find and snap into place without turning on a light.If you'd rather keep more coverage over your nose bridge, our AirFit F20 is the larger ResMed option built for higher pressures. Prefer your hose routed over the top of your head instead of in front of your face? The AirFit F30i does that. All three share the same family of cushion sizes, so switching between them later is straightforward. Browse the rest of our full face CPAP masks to compare. The AirFit F40 requires a prescription, and it's FSA/HSA eligible.