The objective of this study was to evaluate the effect of formulation changes on the temperatures of the reconstituted potato flakes following a standardised microwave reheating using a response surface method. Reconstituted potato flakes with elevated levels of fat (0.6–11.1%), water (69–78.7%) and salt (0–5.7%) were prepared. Thermal properties (thermal conductivity, thermal diffusivity, specific heat capacity) and dielectric properties (dielectric constant, loss factor and penetration depth) were evaluated. The reconstituted potato flakes were reheated in a microwave oven and the temperatures were recorded during and after microwave exposure. Temperatures during reheating decreased with increasing water, butter and salt content. Results show that temperatures during microwave reheating require empirical measurement as opposed to prediction due to changes in composition, thermal and dielectric properties. Reformulation offers the manufacturers an option for altering the temperatures following microwave reheating, however, the magnitude of the formulation changes required may be quite large. The data presented is useful in the preparation of computer models and simulations of microwave heating.