According to the SEM micrographs of the char residue, a dense and intact nanoparticle char layer can be observed for SEBS/IFR/F-OMMT nanocomposite. During combustion, along with the blowing agent of IFR, non-combustible gas was generated by the amino group in F-OMMT, which produced more expanding carbonaceous char. The dense intumescent charred networks can protect the underlying SEBS material and thus improve the flame retardant properties of the composites. Good flame retardant synergistic effects can be realized by the combination of the functional modified montmorillonite and IFR. (DOI: 10.1002/app.44953)