The studies were conducted using the triple intumescent system based on Exolit AP 740 F, which is a synergetic system based on ammonium polyphosphate with the addition of nitrogen-containing compounds. Styrene-acrylic polymer was used as a binder, titanium dioxide acted as a pigment. Plasticizers in the study were selected to assess the influence of their molecular weight on the structure of the foams. Dibutyl phthalate and polybutene oligomers, such as Indopol H 1200, Indopol H 6000 and Indopol H 18000 were selected as plasticizers. The results were presented in the form of images from electronic microscopy, the time of reaching critical temperatures during testing with the help of Bunsen burner, coefficients of swelling of the composition, as well as the diagrams of thermo-gravimetric analysis. The influence of plasticizers on the porous structure of fire resistance of carbon foams of intumescent coatings was established. Using polybutene aliphatic materials as an example, the temperature intervals of the thermo-oxidative destruction of plasticizers were determined, the dependence of their stability during thermal treatment on the value of molecular weight was established. It was shown that the use of plasticizers of different molecular weight enables the change of dimensions of cells of foams by decreasing the indicator of yield limit of the melt, which leads to an increase in the dimensions of these cells. At an increase in molecular weight, the ability of the plasticizer to form associative structures increases, which increases the yield limit of the melt and decreases the value of the average diameter of the foam cells, as well as to change the character of forming formation of contractional cracks in the structure. It was found that the indicator of fire resistance of coatings depends on the type and molecular weight of the used plasticizers. The dependence of fire resistance on molecular weight of the plasticizer for the studied intumescent system based on styrene-acrylic polymer was detected. The results of this research can be used when developing the formulations of fire protective intumescent systems