Compositions based on self-extinguishing expandable vinyl aromatic polymers in granules comprising: a. a polymeric matrix, comprising 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of a copolymerizable monomer; and, homogeneously englobed in the polymeric matrix, b. 3-10% by weight, calculated with respect to the polymer (a), of an expanding system; c. 0.005-5% by weight, calculated with respect to the polymer (a), of a flame-retardant agent consisting of a brominated hydrocarbon containing at least 30% by weight, preferably from 50 to 90% by weight, of bromine; d. 0.001-2% by weight, calculated with respect to the polymer (a), of a synergic additive of the brominated flame-retardant containing a C-C or C-O-O-C thermolabile bond; e. 0.005-5% by weight, calculated with respect to the polymer (a), of at least one additive capable of regulating the cell structure after expansion of the granule and inhibiting the thermal degradation of the brominated flame-retardant, selected from the group consisting of: i. pyrophosphates having the general formula X-P 2 O 7 wherein X represents an alkaline or alkaline earth metal, an ammonium group or a unit deriving from melamine; ii. melamine polyphosphate; iii. partially or completely salified polycarboxylic acids; iv. citrates of alkaline or alkaline earth metals; v. polyfunctional alcohols with 2 or more alcohol functions; vi. esters of polyfunctional alcohols. a. a polymeric matrix, comprising 50-100% by weight of one or more vinyl aromatic monomers and 0-50% by weight of a copolymerizable monomer; and, homogeneously englobed in the polymeric matrix, b. 3-10% by weight, calculated with respect to the polymer (a), of an expanding system; c. 0.005-5% by weight, calculated with respect to the polymer (a), of a flame-retardant agent consisting of a brominated hydrocarbon containing at least 30% by weight, preferably from 50 to 90% by weight, of bromine; d. 0.001-2% by weight, calculated with respect to the polymer (a), of a synergic additive of the brominated flame-retardant containing a C-C or C-O-O-C thermolabile bond; e. 0.005-5% by weight, calculated with respect to the polymer (a), of at least one additive capable of regulating the cell structure after expansion of the granule and inhibiting the thermal degradation of the brominated flame-retardant, selected from the group consisting of: i. pyrophosphates having the general formula X-P 2 O 7 wherein X represents an alkaline or alkaline earth metal, an ammonium group or a unit deriving from melamine; ii. melamine polyphosphate; iii. partially or completely salified polycarboxylic acids; iv. citrates of alkaline or alkaline earth metals; v. polyfunctional alcohols with 2 or more alcohol functions; vi. esters of polyfunctional alcohols. i. pyrophosphates having the general formula X-P 2 O 7 wherein X represents an alkaline or alkaline earth metal, an ammonium group or a unit deriving from melamine; ii. melamine polyphosphate; iii. partially or completely salified polycarboxylic acids; iv. citrates of alkaline or alkaline earth metals; v. polyfunctional alcohols with 2 or more alcohol functions; vi. esters of polyfunctional alcohols.