Description BMC masks are compatible with the machines and pipes from other brands. The BMC full face mask F5 forms part of the newest full face series, with a forehead rest for added support for side sleepers. F5  mask has the full configuration, such as: The grooved cushion provides auto-adaption to your nose bridge resulting in lower air leakage and less pressure on the face. Simple, light weight design. Increased comfort with single layer cushion. The position of the Anti-asphyxia valve results in a smaller elbow and therefore increased convenience. Required for new CPAP, Auto CPAP and Bipap users. Note: Size depends on face length. Distance between eyes and below lips. (S) Small = 8 ~ 9 cm (M) Medium = 9 ~ 10 cm (L) Large = 10 ~ 11.5 cm