Abstract: An enclosure for an electronic device forms a barrier to electro-magnetic radiation. A typical cross-section of the enclosure comprises three parallel layers. The outer and inner surface layers are of a polymeric base material in which is suspended an electrically conductive fill material, giving the surface layers relatively high electrical conductivity. The middle layer is of a polymeric base material, in which is suspended fill material having high magnetic permeability, giving the middle layer relatively high magnetic permeability. In the preferred embodiment, the enclosure is constructed using a co-injection molding process. Nickel-coated graphite (high conductivity) in a polymeric base is injected into a mold from the outer co-injection nozzle, while carbonyl iron powder (high permeability) in a polymeric base is injected into the mold from the inner co-injection nozzle.