In the fusing of electrophotographic prints, the spreading and coalescence of individual toner particles and levelling of films are driven by surface tension and determine the optical parameters of dot gain and gloss as well as print adhesion. In this study a laboratory method has been developed to monitor in-situ the spreading of individual toner particles during heating, and extract the corresponding evolution in particle diameter and contact angle. This method was employed to study different toner particles as a function of temperature, heating rate, and substrate surface energy. Significant differences in spreading extent and rate for the different toner particles were observed, especially on higher energy surfaces, and explained in terms of their dispersive and polar interactions.This study was combined with Xeikon printing trials using systematic variations in the fusing type and degree. The prints were analysed with interferometric profilometry to quantify the response of toner layer thickness and surface topography to the fusing conditions. In particular, spectral decomposition of surface roughness revealed interesting correlations to print gloss.