Synergistic effects of kaolin clay and wollastonite on thermal performance of intumescent fire retardant coatings have been investigated. IFRC-5 showed the substrate temperature 113 °C after 1 h fire test and char expansion 8.5 times higher compared to the control formulation. A 5 wt% increase of fillers in the formulation IRFC-5, carbon contents in char residue increased to 50.67% and oxygen contents reduced to 27.73%. Pyrolysis GC–MS confirmed the fillers reduced the gaseous products from 3.4e+07 to 1.08e+07 in IFRC-5. The fillers in IFRC-5 increased the residual weight up to 46.5 wt.% from 31 wt.%.