Low amounts (<7.5 wt%) of organically modified layered silicate (LS) as well as large amounts (>10 wt%) of spherical amorphous SiO2 (sSiO(2)) has been used successfully as adjuvants in commercial polymeric materials flame retarded with metal hydroxide. The combination of LS and SiO2 is investigated in different thermoplastics with respect to their fire behavior, particular to overcome the restrictions in maximum and minimum filler contents know for the single additives. The aim was to check the potential of combinations of the inert fillers in absence of a real fire retardant. The combination of LS and sSiO(2) harbors the potential for flame retardancy effects close to superposition or even synergy, due to an improved structure of the fire residue. LS-sSiO(2) combinations are proposed to work as adjuvants superior to LS and sSiO(2) in flame retarded polymeric materials. (C) 2016 Society of Plastics Engineers