CPAP chin straps secure the cpap mask to the patients head making it easier to sleep.  The general category of CPAP headgear includes the CPAP chin strap.

CPAP patients using a full faced CPAP mask generally do not requie a CPAP chin strap.  The full face CPAP mask typically includes a small lip into which the chin is placed.  This aids in keeping the mouth closed while the patient sleeps.

Patients using CPAP nasal pillow masks or CPAP nasal masks often require a CPAP chin strap.  The CPAP chin strap helps keep the mouth closed during sleep to keep air from exiting or entering through the mouth.