Abstract: A flexible duct forming apparatus and method in which flexible strip material is wrapped on a rotating mandrel in a helical path, with the edges of the flexible strip material overlapping a pre-determined amount. Reinforcing wire is formed into a helix of substantially constant diameter and pitch and guided by a fixed helical means between the overlapping edges of the flexible strip material. The overlapping edges of the flexible strip material is then pressed around the reinforcing wire to seal and encapsulate the wire to continuously form flexible duct. The reinforcing wire is formed into the substantially constant helix by a fixed helical means which is interchangeably mounted on a base as is the mandrel, so that the apparatus can be used to manufacture different diameter flexible ducting.