A method for forming an impeller for a pump provides a reliable protective barrier that prevents or eliminates the ingress of pumped fluid that might otherwise attack the magnetic assembly of the impeller. An inner barrier is hermetically connected to an internal impeller section at one or more seams to cover at least part of a first magnetic assembly. Filler is introduced into a spatial volume of the first magnet assembly associated with the internal impeller section. The remainder of an impeller is molded over or in association with the internal impeller section to form the impeller with the inner barrier and an outer barrier overlying the inner barrier for protection of the first magnet assembly from the pumped fluid.