Expandable, thermoplastic polymer bead material, comprising A) from 45 to 97.8 percent by weight of a styrene polymer, B1) from 1 to 45 percent by weight of a polyolefin with a melting point in the range from 105 to 140° C., B2) from 0 to 25 percent by weight of a polyolefin with a melting point below 105° C., C1) from 0.1 to 25 percent by weight of a block or graft copolymer with weight-average molar mass Mw of at least 100,000 g/mol, comprising a) at least one block S composed of from 95 to 100% by weight of vinylaromatic monomers and from 0 to 5% by weight of dienes, and b) at least one copolymer block (S/B)A composed of from 63 to 80% by weight of vinylaromatic monomers and from 20 to 37% by weight of dienes, with glass transition temperature TgA in the range from 5 to 30° C., where the proportion by weight of the entirety of all of the blocks S is in the range from 50 to 70% by weight, based on the block or graft copolymer A, C2) from 0 to 20 percent by weight of a styrene-butadiene or styrene-isoprene block copolymer different from C1, C3) from 0.1 to 9.9 percent by weight of a styrene-ethylene-butylene block copolymer, D) from 1 to 15 percent by weight of a blowing agent, and E) from 0 to 5 percent by weight of a nucleating agent, where the entirety composed of A) to E) gives 100% by weight.