A breath powered positive airway pressure device having an expiratory chamber for receiving expired air from a user. The chamber has at least one resiliently flexible surface that is configured to expand to accommodate the expired air, so that the pressure within the chamber gradually increases during expiration. The device may also include an inspiratory chamber for holding air to be inspired, wherein the at least one resiliently flexible surface forms a flexible partition separating the expiratory chamber from the inspiratory chamber. The flexible partition is configured to expand into the inspiratory chamber during expiration, so that the air that is held within the inspiratory chamber also becomes pressurized during expiration.
