The Transient Plane Source (HotDisk) Method employs a sensor of electrically conducting nickel, reinforced by layers of insulating Kapton. The sensor is placed between two identical samples. A current is applied to the sensor which generates heat and the sensor can monitor the temperature vs time. By monitoring the sensor’s recorded temperature response versus the time, one can determine the thermal conductivity of the material. Careful consideration needs to be given to setting up the appropriate timing and power parameters as well as in selecting the right size sensor for different types of materials. These challenges can be overcome with experience – but result in some ambiguity with new materials and composites. TAL suggests limiting application of the TPS method to materials that fall neatly within categories defined within the ISO guidance drafted for the TPS technique.