In electrophotography the printed image is fixed by heating. Gloss and toner adhesion require that the paper also heat up. This leads to dimensional instability problems and thus the thermal properties of paper must be optimized for high quality. We explain how the thermal diffusivity of paper can be measured with a thermoacoustic cell. The method detects the delay of thermal waves transmitted through the paper sheet. The method is suitable up to grammages of 160 g/m². Thermal conductivities of measured non-impact printing papers were found to vary from 0.16 to 0.25 W/m·K.