A patient interface for delivering a flow of air at a positive pressure to a patient during sleep, including a cushion assembly, an air conduit (133) comprising a stretchable tube structured to twist when stretched and a decoupling system including first, second and third decoupling structures to decouple tube drag forces as a patient twists and turns. The second decoupling structure includes a ring (128) and elbow (135) with partially spherical contact surfaces which form an airtight ball and socket joint.
