A limb for a breathing circuit manufactured from very thin walled polymer materials has an elongate axial reinforcing spine lying freely inside the conduit and fixed to each end connector. The spine is laterally compliant but axially stiff. The spine provides resistance to tensile and compressive loads on the conduit, including that induced by prevailing internal pressures.

A thin ribbon spirally wound polymer conduit and method of forming, wherein a helical reinforcing bead is interposed adjacent overlapping layers of ribbon. Further, a method of continuously forming spirally wound conduit wherein a sacrificial layer, preferably having a different base polymer to that of the conduit, is first applied to the former before the conduit is formed overtop.

A thin ribbon spirally wound polymer conduit and method of forming, wherein a helical reinforcing bead is interposed adjacent overlapping layers of ribbon. Further, a method of continuously forming spirally wound conduit wherein a sacrificial layer, preferably having a different base polymer to that of the conduit, is first applied to the former before the conduit is formed overtop.