A mask system for use with blowers and flow generators in the treatment of Sleep Disordered Breathing, the mask system comprising: a shroud including headgear connectors adapted to removably attach to respective headgear straps (92, 94) of headgear; an elbow adapted to be connected to an air delivery tube that delivers breathable gas to the patient; and a cushion module comprising: a frame defining a breathing chamber; and a cushion adapted to form a seal with the patient's face, wherein the shroud includes an open construction that provides an annular or part annular retaining portion structured to retain the frame and the elbow; wherein the frame and the cushion are co-molded with one another, the cushion being constructed of a first, relatively soft, elastomeric material and the frame being constructed of a second material that is more rigid than the first material; wherein at least a portion of the cushion includes a concertina section and the concertina section preferably includes a bellows structure with one or more folds; wherein the cushion is a full-face cushion; wherein the elbow includes an anti-asphyxia valve including a flap portion adapted to selectively close a port provided in the elbow depending on the presence of pressurized gas. a shroud including headgear connectors adapted to removably attach to respective headgear straps (92, 94) of headgear; an elbow adapted to be connected to an air delivery tube that delivers breathable gas to the patient; and a cushion module comprising: a frame defining a breathing chamber; and a cushion adapted to form a seal with the patient's face, wherein the shroud includes an open construction that provides an annular or part annular retaining portion structured to retain the frame and the elbow; wherein the frame and the cushion are co-molded with one another, the cushion being constructed of a first, relatively soft, elastomeric material and the frame being constructed of a second material that is more rigid than the first material; wherein at least a portion of the cushion includes a concertina section and the concertina section preferably includes a bellows structure with one or more folds; wherein the cushion is a full-face cushion; wherein the elbow includes an anti-asphyxia valve including a flap portion adapted to selectively close a port provided in the elbow depending on the presence of pressurized gas. a frame defining a breathing chamber; and a cushion adapted to form a seal with the patient's face, wherein the shroud includes an open construction that provides an annular or part annular retaining portion structured to retain the frame and the elbow; wherein the frame and the cushion are co-molded with one another, the cushion being constructed of a first, relatively soft, elastomeric material and the frame being constructed of a second material that is more rigid than the first material; wherein at least a portion of the cushion includes a concertina section and the concertina section preferably includes a bellows structure with one or more folds; wherein the cushion is a full-face cushion; wherein the elbow includes an anti-asphyxia valve including a flap portion adapted to selectively close a port provided in the elbow depending on the presence of pressurized gas.