The ResMed chin strap keeps the mouth closed when you are using a nasal or nasal pillow on CPAP therapy. The pressure delivered from your sleep apnea therapy device can cause the mouth to blow open, especially if you are prescribed a higher setting. Air leaks severely reduce the effects of your prescribed CPAP therapy causing you to wake up with a dry mouth, feeling tired, and needing more rest. Other options to consider for eliminating mouth breathing would be to try a full face style of CPAP that covers the nose and mouth. Waking with mouth dryness could be an indicator that your mouth is falling open during sleep.