This article highlights the importance of ground plasma testing in the design and development of flight experiments for atmospheric reentry vehicles. The determination of catalytic properties covers a key role for Thermal Protection Systems, since flight catalysis phenomenon are often a design driver for the heat shield. The results of a test campaign at the von Karman Institute for Fluid Dynamics, in the framework of the European Space Agency EXPERT reentry mission, are presented. They are dedicated to the determination of the catalytic and emissive properties of the ceramic and metallic Thermal Protection Materials selected for the nose and the body-skirt of the EXPERT capsule respectively. During the reentry, the chemistry developing over the vehicle surface due to the different catalycity properties of the two Thermal Protection Materials can promote a temperature jump at their junction. An experimental evidence of such a phenomenon is also provided.