The present invention relates to a cushion (10) for a patient interface that delivers breathable gas to a patient including a base wall (28) structured to be connected to a frame, an underlying support cushion (30) extending away from the base wall towards the patient's face in use, and a membrane (32) provided to substantially cover at least a portion of the underlying cushion. The membrane (22) is adapted to form a continuous seal on the patient's face. The underlying cushion has a spring-like connection with the base wall. The underlying cushion and/or base wall define a spring constant that varies along a length of the seal. The cushion may be provided in various sizes in order to accommodate various facial sizes. The mouth width is constant for all cushion sizes.
