For very short transients that are 20 milliseconds (ms) or less, the resistor element must handle all the electrical energy. This is because the time period is so short that the heat energy is not able to be transferred  to the surroundings. This is reason why the temperature rise is dependent upon the mass of resistance element. A larger mass resistance element will absorb more energy before it reaches a thermal limit. This is how the all metal construction of the Power Metal Strip® technology provides pulse performance by having a large metal cross-section that does not depend on a substrate. In longer period transients, such as a surge, then the surroundings begin to contribute to the energy capability. The heat energy is transferred from the resistance element into the terminations. For Short Time Overload conditions, the surroundings contribute to the overall energy handling.