The necessity to study the thermophysical properties of porous inorganic materials is due to the wide use of thin-walled structures, the fire protective coating of which is performed when use porous materials. One of the most dangerous physical influence, leading to the destruction of thin-walled constructions in a fire, is a rapid increase in the temperatures of the combustion products in the fire zone. For a fire fencing, just 20÷30 minutes after its start, the temperature of the products in the combustion zone can reach 800÷900 °C, while the temperature can increase under more favorable conditions for the combustion process of air exchange. For open fires, when the air exchange conditions are not limited, the temperature of the combustion products can quickly reach 1100 °C of more. In the article, analyzing the effect on the porous materials of high-temperature combustion products, high humidity, direct exposure to water, as well as the process of phase of phase transitions of moisture contained in capillaries and its possible consequences. Presented and analyzing the influence of the process of thermal radiation inside gas-filled cellular structures on the heat-conducting properties of porous material based on perlite and expanded vermiculite. The results of an experiment to study the dependence of the thermal conductivity coefficient of expanded vermiculite on the specific particle size density and pressure suggest that with an increase in the temperature of the combustion products a thin-walled fire protection layer made of fibrous materials (for example, perlite and expanded vermiculite) with a decrease in the size of the solid fraction, the thermal conductivity coefficient of expanded vermiculite increases to a greater extent than of perlite, nab a certain tendency is observed to increase the share of the convective component in the thermal conductivity of expanded fire-protective materials as the particle sizes of their solid fraction decrease.