An apparatus for manufacturing a flexible tubular duct includes a mandrel, and a substrate feeding assembly for feeding a strip of flexible substrate material to the mandrel. Apparatus is provided for bending the strip of substrate material to have a rounded encapsulating portion, into which is fed a stream of loose fibrous insulating material. A mechanism is further provided for delivering an elongate reinforcing element onto the strip of flexible substrate material. In operation, the rounded encapsulating portion and the reinforcing element are wound in a helical path around the mandrel so that the loose fibrous material is encapsulated as a core in the helically wound rounded encapsulating portion the reinforcing element is also encapsulated by the strip of substrate material, whereby to form a reinforced flexible tubular duct.