A positioning and stabilising structure to provide a force to hold a seal-forming structure in a therapeutically effective position on a patient's head for positive pressure airway treatment of sleep disordered breathing, the positioning and stabilising structure comprising: at least one gas delivery tube to deliver a flow of air to an entrance of the patient's airways via a seal-forming structure, each gas delivery tube being constructed and arranged to contact, in use, at least a region of the patient's head superior to an otobasion superior of the patient's head, each gas delivery tube comprising a laminate construction with a plurality of layers, with an inner layer (9375, 9385) of air-impermeable material defining a tube wall defining a hollow interior through which air is able to flow to the seal-forming structure, each gas delivery tube comprising: a superior tube portion configured to extend in use from a position on top of the patient's head to a position along the side of the patient's head or face, the superior tube portion comprising 1) a textile material layer and/or a foam material layer, and 2) the air-impermeable material layer (9375, 9385) provided to the textile material layer and/or the foam material layer to make the superior tube portion substantially air-impermeable; and an inferior tube portion configured to extend from the position along the side of the patient's head or face to a position adjacent the entrance to the patient's airways, the inferior tube portion comprising 1) a textile material layer and/or a foam material layer, and 2) the air-impermeable material layer (9375, 9385) provided to the textile material layer and/or the foam material layer of the inferior tube portion to make the inferior tube portion substantially air-impermeable, wherein one of the inferior tube portion and superior tube portion has a greater rigidity than the other of the inferior tube portion and superior tube portion. at least one gas delivery tube to deliver a flow of air to an entrance of the patient's airways via a seal-forming structure, each gas delivery tube being constructed and arranged to contact, in use, at least a region of the patient's head superior to an otobasion superior of the patient's head, each gas delivery tube comprising a laminate construction with a plurality of layers, with an inner layer (9375, 9385) of air-impermeable material defining a tube wall defining a hollow interior through which air is able to flow to the seal-forming structure, each gas delivery tube comprising: a superior tube portion configured to extend in use from a position on top of the patient's head to a position along the side of the patient's head or face, the superior tube portion comprising 1) a textile material layer and/or a foam material layer, and 2) the air-impermeable material layer (9375, 9385) provided to the textile material layer and/or the foam material layer to make the superior tube portion substantially air-impermeable; and an inferior tube portion configured to extend from the position along the side of the patient's head or face to a position adjacent the entrance to the patient's airways, the inferior tube portion comprising 1) a textile material layer and/or a foam material layer, and 2) the air-impermeable material layer (9375, 9385) provided to the textile material layer and/or the foam material layer of the inferior tube portion to make the inferior tube portion substantially air-impermeable, wherein one of the inferior tube portion and superior tube portion has a greater rigidity than the other of the inferior tube portion and superior tube portion.