A patient interface device including a cushion assembly having a cushion-in-a-cushion arrangement and a system for supplying a flow of gas to a patient using such an interface device. The patient interface includes a mask shell having a patient side and an outer side opposite the patient side adapted...http://www.google.es/patents/US7287528?utm_source=gb-gplus-sharePatente US7287528 - Cushion inside a cushion patient interface
