  We show that by a simple two-steps measurement protocol one can extract the
thermal properties of anisotropic insulator materials. We focus on Bi2Se3
single crystal, a layered crystal with individual sheets held together by Van
der Waals force, presenting strong heat diffusion anisotropy. Since the shape
of the sample does not allow experiments in the perpendicular direction the
challenge is to measure the in plane and out of plane thermal properties by in
plane measurements. The optical properties of Bi2Se3 being known (opaque sample
for the pump and probe beams), thermoreflectance microscopy experiments can be
done on the bare substrate. In this case, the lateral heat diffusion is
governed by the in plane thermal diffusivity. A 100 nm gold layer is then
deposited on the sample. In this second experiment it is straightforward to
demonstrate that the perpendicular thermal properties of the layer rule the
lateral diffusivity. The good agreement of theoretical curves obtained by
thermal models with experimental data permit us to evaluate the thermal
conductivity coefficients of bulk Bi2Se3.
