An air delivery system (30) for providing a supply of air from a source of air at positive pressure to an interfacing structure (20) located at the entrance to the airways of a patient includes a manifold (70) adapted to connect with the supply of positive air pressure and at least one tube (42) connected to the manifold (70) and adapted to deliver the supply of air to the interfacing structure (20). Each tube (42) is structured to allow movement between (1) an open phase in which the tube (42) allows the passage of air and (2) a collapsed phase in which the tube (42) is collapsed. Each tube (42) is structured such that weight of a typical patient's head against bedding apparel is sufficient to collapse the tube (42) from the open phase to the collapsed phase.
