A patient interface system for delivery of a supply of air at positive pressure to the entrance of a patient's airways for treatment of sleep disordered breathing includes an air delivery tube connected to a flexible portion of a plenum; a vent structure having sufficient rigidity to support its own weight under gravity and/or not to block or fold under tube movement or tube drag; and a patient interface structure. The patient interface structure includes a seal forming structure arranged on a top portion of the plenum; and a seal positioning and stabilizing structure connected to a flexible portion of the plenum. The seal-forming structure is substantially decoupled from a tube drag force.