A patient interface system comprising: > an interface portion adapted to create a seal with at least a nose of a user; > a coupling that permits the patient interface system to be coupled to a gas delivery system; > a headgear system that allows the interface portion to be positioned and retained on a head of the user with the headgear system providing a transformational locking behavior with an ability to transform from an elastic type elongation behavior to a generally non-elongating type behavior when the patient interface system is in use, the headgear system comprising > a mechanically based directional lock , > one or more non-elongating elements having sufficient stiffness or column strength to pass through the mechanically based directional lock without significant buckling, and > an elastic element , > the elastic type elongation behavior being provided by the elastic element , > the elastic element being configured to provide a retraction force, > the transformational locking behavior being provided by the mechanically based directional lock , > the mechanically based directional lock being configured to apply a friction force on the one or more non-elongating elements in use, and » to automatically allow movement in a retraction direction at a first level of resistance achieved by the retraction force of the elastic element against the first level of resistance offered by the mechanically based directional lock and » allow movement in an elongation direction at a second level of resistance offered by the mechanically based directional lock higher than the first level of resistance, or prevent movement in the second direction. > an interface portion adapted to create a seal with at least a nose of a user; > a coupling that permits the patient interface system to be coupled to a gas delivery system; > a headgear system that allows the interface portion to be positioned and retained on a head of the user with the headgear system providing a transformational locking behavior with an ability to transform from an elastic type elongation behavior to a generally non-elongating type behavior when the patient interface system is in use, the headgear system comprising > a mechanically based directional lock , > one or more non-elongating elements having sufficient stiffness or column strength to pass through the mechanically based directional lock without significant buckling, and > an elastic element , > the elastic type elongation behavior being provided by the elastic element , > the elastic element being configured to provide a retraction force, > the transformational locking behavior being provided by the mechanically based directional lock , > the mechanically based directional lock being configured to apply a friction force on the one or more non-elongating elements in use, and » to automatically allow movement in a retraction direction at a first level of resistance achieved by the retraction force of the elastic element against the first level of resistance offered by the mechanically based directional lock and » allow movement in an elongation direction at a second level of resistance offered by the mechanically based directional lock higher than the first level of resistance, or prevent movement in the second direction. » to automatically allow movement in a retraction direction at a first level of resistance achieved by the retraction force of the elastic element against the first level of resistance offered by the mechanically based directional lock and » allow movement in an elongation direction at a second level of resistance offered by the mechanically based directional lock higher than the first level of resistance, or prevent movement in the second direction. <EOS>