This paper deals with the problems faced during the research on the insulating structures used in the thermal shielding of flight recorders. These structures are characterised by specific properties determined by, among other aspects, their porosity. The complex and coupled heat-exchange phenomena occurring under the operating conditions of the recorders, and in numerous cases combined with mass exchange, require dedicated test methods. The paper characterises the origin of the research problem, presents a methodology for comprehensive testing of the thermal propertiesand uses the example of determining the insulating properties of the Promalight microporous structure ®-1000R. The authors focussed on thermal diffusivity tests performed by means of the oscillatory excitation method. The measurements were conducted on a test stand to determine the effect the type of gas filling had on the porous structure and the pore filling gaspressure effect on the temperature characteristics of apparent thermal diffusivity. The authors also conducted research on the structure’s resistance to direct flame exposure. The analysis of the obtained results enable recognition and characterisation of the key phenomena of heat and mass transfer; the numerical results exert a significant influence on their application.