A mask cushion or a mask assembly therewith provides a comfortable and effective seal for provision of a gas therapy by a respiratory treatment apparatus. The mask cushion (102) may be integrated with or coupled to a mask frame. The mask cushion typically includes an inner cushion component (104). The mask cushion also includes a patient facial-contact side portion with a chamber (108) and a barrier (106) to form the chamber that may be flexible. The chamber may serve as an outer layer with respect to the inner cushion component. The chamber may be partially or completely filled with a gas, fluid or gel. The inner cushion may be formed with a soft flexible material such as an elastomer or foam, etc. The barrier may be a membrane and may also be soft flexible material.