Expandable granulates, having compositions based on vinyl-aromatic polymers, essentially consisting of: a) 65-99.8% by weight of a copolymer obtained by polymerizing 85-100% by weight of one or more vinyl-aromatic monomers having general formula and 0-15% by weight of an α-alkylstyrene in which the alkyl group contains from 1 to 4 carbon atoms; b) 0.01-20% by weight, calculated with respect to the polymer (a), of a carbon black having an average diameter ranging from 10 to 1000 nm and a surface area ranging from 5 to 200 m 2 /g; c1) 0.01-5% by weight, calculated with respect to the polymer (a), of graphite selected from natural or synthetic graphite having an average diameter ranging from 0.5 to 50 μm and a specific area of 5-20 m 2 /g, or expandable graphite; and at least one of the following additives -: c2) 0.01-5% by weight, calculated with respect to the polymer (a), of oxides and/or sulfates and/or lamellar dichalcogenides of metals of groups IIA, IIIA, IIB, IVB, VIB or VIIIB, c3) 0.01-5% by weight, calculated with respect to the polymer (a), of inorganic derivatives of silicon of the lamellar type; d) 0.01-4.5% by weight, calculated with respect to the polymer (a), of a nucleating agent; and e) 1-6% by weight, calculated with respect to.100 parts of the total of (a)-(d), of one or more expanding agents; wherein Formula is wherein n is zero or an integer ranging from 1 to 5 and Y is a halogen, such as chlorine or bromine, or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms. a) 65-99.8% by weight of a copolymer obtained by polymerizing 85-100% by weight of one or more vinyl-aromatic monomers having general formula and 0-15% by weight of an α-alkylstyrene in which the alkyl group contains from 1 to 4 carbon atoms; b) 0.01-20% by weight, calculated with respect to the polymer (a), of a carbon black having an average diameter ranging from 10 to 1000 nm and a surface area ranging from 5 to 200 m 2 /g; c1) 0.01-5% by weight, calculated with respect to the polymer (a), of graphite selected from natural or synthetic graphite having an average diameter ranging from 0.5 to 50 μm and a specific area of 5-20 m 2 /g, or expandable graphite; and at least one of the following additives -: c2) 0.01-5% by weight, calculated with respect to the polymer (a), of oxides and/or sulfates and/or lamellar dichalcogenides of metals of groups IIA, IIIA, IIB, IVB, VIB or VIIIB, c3) 0.01-5% by weight, calculated with respect to the polymer (a), of inorganic derivatives of silicon of the lamellar type; c2) 0.01-5% by weight, calculated with respect to the polymer (a), of oxides and/or sulfates and/or lamellar dichalcogenides of metals of groups IIA, IIIA, IIB, IVB, VIB or VIIIB, c3) 0.01-5% by weight, calculated with respect to the polymer (a), of inorganic derivatives of silicon of the lamellar type; d) 0.01-4.5% by weight, calculated with respect to the polymer (a), of a nucleating agent; and e) 1-6% by weight, calculated with respect to.100 parts of the total of (a)-(d), of one or more expanding agents; wherein Formula is wherein n is zero or an integer ranging from 1 to 5 and Y is a halogen, such as chlorine or bromine, or an alkyl or alkoxyl radical having from 1 to 4 carbon atoms.