An apparatus for providing positive pressure respiratory therapy to a patient breathing in a respiratory cycle including an inhalation portion and an exhalation portion, said apparatus comprising: a controllable motor-blower configured to generate a supply of air at a positive pressure relative to ambient pressure by rotating an impeller at an impeller speed, a housing holding said motor-blower, the housing comprising an inlet and a patient-connection port, the patient-connection port being structured to communicate said supply air at said positive pressure from the motor-blower to a patient interface via an air circuit in use; a sensor to monitor at least one of pressure and a flow rate of the supply of air at positive pressure and to generate a sensor output; and a controller configured to adjust an operating parameter of said motor-blower in accordance with said sensor output to maintain a minimum positive pressure in said patient interface during a treatment session by causing an increase in the impeller speed during the inhalation portion of the respiratory cycle and causing a decrease in the impeller speed during the exhalation portion of the breathing cycle, the air circuit comprising: a tubular structure; the tubular structure having a circular woven structure; the tubular structure being seamless along a length of the tubular structure; the tubular structure including a plurality of warp threads and a plurality of weft threads; the plurality of weft threads including a first monofilament weft thread and a second monofilament weft thread; the first monofilament weft thread being located adjacent to at least one non-monofilament weft thread, the second monofilament weft thread also being located adjacent to at least one non-monofilament thread; and wherein the at least one non-monofilament thread is located between the first monofilament weft thread and the second monofilament weft thread. a controllable motor-blower configured to generate a supply of air at a positive pressure relative to ambient pressure by rotating an impeller at an impeller speed, a housing holding said motor-blower, the housing comprising an inlet and a patient-connection port, the patient-connection port being structured to communicate said supply air at said positive pressure from the motor-blower to a patient interface via an air circuit in use; a sensor to monitor at least one of pressure and a flow rate of the supply of air at positive pressure and to generate a sensor output; and a controller configured to adjust an operating parameter of said motor-blower in accordance with said sensor output to maintain a minimum positive pressure in said patient interface during a treatment session by causing an increase in the impeller speed during the inhalation portion of the respiratory cycle and causing a decrease in the impeller speed during the exhalation portion of the breathing cycle, the air circuit comprising: a tubular structure; the tubular structure having a circular woven structure; the tubular structure being seamless along a length of the tubular structure; the tubular structure including a plurality of warp threads and a plurality of weft threads; the plurality of weft threads including a first monofilament weft thread and a second monofilament weft thread; the first monofilament weft thread being located adjacent to at least one non-monofilament weft thread, the second monofilament weft thread also being located adjacent to at least one non-monofilament thread; and wherein the at least one non-monofilament thread is located between the first monofilament weft thread and the second monofilament weft thread. a tubular structure; the tubular structure having a circular woven structure; the tubular structure being seamless along a length of the tubular structure; the tubular structure including a plurality of warp threads and a plurality of weft threads; the plurality of weft threads including a first monofilament weft thread and a second monofilament weft thread; the first monofilament weft thread being located adjacent to at least one non-monofilament weft thread, the second monofilament weft thread also being located adjacent to at least one non-monofilament thread; and wherein the at least one non-monofilament thread is located between the first monofilament weft thread and the second monofilament weft thread.