This paper describes the experimental characterization of the thermal insulation properties of a multilayer insulator (MLI) and of an aerogel. Materials characterization was performed to optimize the thermal control design of a small interferometer devoted to planetary observation. In order to simulate the Martian environment, tests were performed in a carbon dioxide atmosphere, with pressures between 10 and 104 Pa and temperatures from 193 to 353 K. MLI was tested at different levels of layers compression to investigate thermal insulation changes deriving from the constraining of the mechanical structure. The thermal conductivity was measured with a purposely designed guarded hot plate apparatus. Results showed that the aerogel exhibits a lower thermal conductivity for gas pressures larger than 100 Pa and that the layer compression of the MLIs does not affect the heat conduction for gas pressures above 103 Pa.