A method is described for forming a flow nozzle whose cross section varies smoothly from one shape to another. The flow passage consists of fiber glass cloth saturated with epoxy resin cast in place about an elastic water filled rubber diaphragm. An example of such a nozzle, with a circular inlet section and a rectangular exit section was constructed and incorporated in a wind-tunnel design. The flow distribution, excluding the exit boundary layer, is uniform to within 0.5 percent. The exit boundary layer is laminar and steady and the discharge coefficient is 0.989.