The present invention discloses an expandable vinyl aromatic polymer comprising: a) a matrix of a vinyl aromatic polymer, b) 1-10% by weight, calculated with respect to the polymer (a), of a blowing agent embedded in the polymeric matrix, c) 0.1 to 5% by weight, calculated with respect to the polymer (a), of talcum having a D50 particle size, measured by sedigraph (ISO 13317-3), of between 2.3 and 5 μm and a BET specific surface area, measured according to DIN 66131/2, of between 4.2 and 9.5 m2/g, d) 0.1 to 6% by weight, calculated with respect to the polymer of carbon black with a BET specific surface area, measured according to ASTM D-6556, of between 9 and 65 m2/g, e) 0.1 to 1% by weight, calculated with respect to the polymer (a), of polyethylene wax homogeneously distributed in the polymeric matrix.