The relation between heat flow through snow and microstructure is crucial for the comprehension and modeling of thermophysical, chemical, and mechanical properties of snow. This relationship was investigated using heat flux measurements combined with a microstructural numerical approach. A snow sample was subjected to a temperature gradient and the passing heat flux was measured. Simultaneously, the snow microstructure was imaged by X-ray micro-tomography. The heat flow through the observed ice matrix and its heat conductivity was computed by a finite element method. Comparison of measured and simulated heat conductivities suggests that heat conduction through the ice matrix is predominant. The representative elementary volume with respect to density and heat conductivity as well as the tortuosity factor of the ice matrix was determined. In contrast to the density, the tortuosity factor takes into account the relevant geometry of the ice matrix and has many advantages in heat transfer models.