Rigid polyurethane (RPU) foams have been effectively modified with various intumescent flame retardants (IFR) of ammonium polyphosphate/sepiolite/melamine. This study aims to examine the morphologies and fire behaviour of RPU foams by exploring the potential of sepiolite as a novel carbonizing agent in an IFRs system. The effect of various amounts of IFR constituents on RPU foams was investigated. SEM images showed a more stable structure and lesser cell size in the RPUF composite with the incorporation of IFRs compared to that of pure RPUF. The results of the limiting oxygen index (LOI) test showed that 16 phr IFR in a mass ratio of 1:2:1 enhanced the LOI value of the composite by 23.20 % compared to pure RPUF. From the UL-94 analysis, the grade V-0 was obtained for RPUF/IFR 16 phr (1:2:1) and the lowest after-flame time after ignition of 21.4 s was recorded at this formulation compared to other IFR ratio and content used. All IFR components were observed to have contributed to the boosted flame retardancy of the RPUF. The findings of this study confirm that IFRs of ammonium polyphosphate/sepiolite/melamine enhance the interaction between the IFR and the foam matrix and have boosted the flame retardancy of RPU foam composites. There is a strong potential that the RPUF composite developed can be used as insulation material.