Hey Jack,
I am a Neonatal Nurse from Australia, I designed a NEO-prene ( a very soft, non stretch neoprene) Chin Strap to go with my NEO-prene CPAP Cap. it attaches to the rim of the cap with double sided loop/hook fasteners. It is very comfortable & very effective for stopping 'Pop off'.
Please do not hesitate to contact me if you require any further information. austranter@grapevine.com.au
I will attach a photo of it in use. The Cap pictured is compatible with F&P CPAP. Caps are available for other CPAP devices.
Regards,
Bev