Various components of thermal systems are shown molded within a polymer composite sheath, including heaters, sensors, and control circuits. The use of transfer and compression molding allows for the use of thermoset polymers containing very high levels of reinforcement fillers. These improved materials, in turn, create a component with superior thermophysical properties, including high heat flux levels, thermal conductivity, impact resistance, corrosion resistance, and maintenance of mechanical properties at high temperatures (>300.degree. F.). The present invention also allows for wide variety of geometric configurations and the possibility to insert temperature sensors directly in hot zones of heaters.