Thank you for contacting CPAP SUPPLYUSA.COM
It sounds like you may be more comfortable at times breathing through your mouth. The full face mask will allow you to breathe comfortably through your nose or mouth. You should get the humidity you need when you wear the full face mask, where as with a nasal mask,even with a chin strap, you can open your mouth and be breathing dry air.
Good luck wtih the full face mask and contact us again if we can be of further help.
Debbie Shirley,RRT