THERMAL PROPERTIES. As a result of the ever increasing integration of electromagnetic and mechanical components within an ever-decreasing space, more and more reject heat is generated, which, in turn, places greater demands on the thermal properties of plastics. With suitable fillers, the thermal conductivity of plastics can be varied over a wide range. In addition, fillers can reduce the cooling time during the injection moulding process and produce moulded parts with increased thermal conductivity in preferred directions.