The results of thermal resistance of fire-retardant materials "OGNEBASALT" PMBOR and OGNEZA-GT sealant in the form of a mineral wool heat-insulating plate are presented. To study the behavior of fire-retardant materials, the method of TG-DSC synchronous thermal analysis (thermogravimetry in conjunction with differential scanning calorimetry) was used on a NETZSCH thermal analyzer. The incombustible properties of "OGNEBASALT" PMBOR have been confirmed, which showed a decrease in the mass of the material by 21 % when heated to 1000 °C. The thermo-expanding sealant OGNEZA-GT reduced its weight at the same heating with the fire-basalt material by 64 %. For a 10 % weight loss, the two test specimens require different temperatures of 395 and 262 °C, respectively. Time interval of "OGNEBASALT" PMBOR weight loss from 99.6 % to 77.6 % – from 12 minutes to 27 minutes of the experiment; for OGNEZA-GT sealant, from 99.8 % to 54.7 % – from 8 minutes to 18 minutes of testing. The best thermo-resistant properties have been revealed for the fire-retardant material "OGNEBASALT" PMBOR, which makes it possible to recommend its widespread use as a material for passive fire protection. The research results can be used to justify the choice of fire protection in buildings of various functional classes of fire hazard.