Abstract: A breathing circuit for providing conduit from a breathing apparatus or anaesthetic device to a patient, the breathing circuit being generally coaxial and including a first flexible tube and a second flexible tube inside the first flexible tube. The first flexible tube has a smooth inner surface and a reinforcing cord or ribbing along its length and integral around its outer surface. The first flexible tube has a relatively thin wall with the cord, which is preferably in a spiral, providing structural strength or stiffness while retaining flexibility.