Thermal properties are examined based on measured data for precise estimation of heat transfer phenomena in fusing region in electrophotographic printers. Measurement of the surface texture of paper indicates the existence of air due to the surface roughness of the paper, and the thickness of an equivalent air gap layer as a thermal resistance in heat conduction is evaluated based on the surface profile. The amount of air existing in a toner layer due to its porous feature is determined based on the particle arrangement and the diameter of toner particles, from which another additional thermal resistance due to air is evaluated. Numerical estimations of temperature field with and without the additional thermal resistance indicate that the introduction of the thermal resistance evaluated in this paper contribute to a marked improvement of the estimation. The importance of appropriate position for introducing the thermal resistance is also pointed out.