A theoretical model of the flash fusing process for electrophotographic machines was developed using the joint solution of a nonlinear circuit equation and the one-dimensional thermal diffusion equation. Numerous experiments were run using different toners according to the size of toner particles and the pulse width in order to determine the minimum energy that was required for fusing. The experiments confirm that this model predicts reasonably well what was observed in the lab. The melt depth required for good fusing is slightly less than mean particle size. At that depth the temperature is somewhat greater than the temperature required in the nip of a hot roll fuser for the same toner. Under typical flash fusing, the top surface of the toner is subjected to considerably higher temperatures than the melt temperature of the toner. From the combined analytical and experimental results, the proper compromises can be made for efficiency and volatiles.