A composite strip 10 windable to form a helical pipe is disclosed. The composite strip 10 comprises: an elongate plastic strip 11 having a base portion 12 and at least one lengthwise extending rib portion 20 upstanding from the base portion 12; and an elongate reinforcing strip 30 extending lengthwise and supported laterally by the rib portion 20, the reinforcing strip 30 having a height to thickness ratio of at least three to one and orientated substantially perpendicular to the base portion 12. When wound into a helical pipe, the reinforcing strip 30 reinforces the pipe against radial crushing loads. A bead 40 seals the reinforcing strip 30 from the environment. Desirably the composite strip 10 further comprises: a planar lamina 50 extending lengthwise and bonded to the base portion 12, the lamina 50 having a higher Young's modulus and strength than those of the plastic strip 11. The lamina 50 greatly improves the pressure rating of a pipe wound from the strip 10.