The high power density and stability are a result of the construction that maximizes heat transfer from the resistance element to the PCB. The key features are: a thin layer of thermal film that electrically isolates the resistance element from the copper heat spreader plates that provides a short efficient thermal path. Secondly, large copper plates that distribute heat from the resistance element into the PCB, which reduces hotspot temperature extremes and improves long term resistance element stability. Finally, Nickel Chromium resistance alloy for the B version provides a thicker more robust resistive plate as compared to other constructions. Together, these three construction features of the WFM provide the increased power density and long term performance benefits.