Abstract: An impeller for a radial flow device selected from the group consisting of radial--and mixed-flow compressors, pumps and turbines which is designed for both aerodynamic performance and manufacturability at high production rates. The mean blade surface of the impeller is substantially helical, as the angle of any point on the mean blade surface relative to a meridional plane passing through the axis of rotation of the impeller varies linearly with the radius and z-axis location of that point relative to an arbitrary radial plane z.sub.0. A single-piece mold for making the impeller, and a method for making the mold, are also disclosed. The impeller can made in a high-speed molding process without significant post-production processing, and it can be easily withdrawn from a mold without destruction or disassembly of the mold.