Expandable styrene polymers

An expandable styrene polymer for elastic polystyrene foams, comprising

• a) from 75 to 98% by weight of polystyrene and/or a styrene copolymer containing at least 50% by weight of copolymerized styrene,
• b) from 2 to 25% by weight of at least one styrene-soluble elastomer comprising polybutadiene rubber havinga molecular weight of from 200,000 to 300,000 and containing less than 50% of 1,4-cis structures and from 5 to 20 percent of 1,2-vinyl structures or from 50 to 99 percent of 1,4-cis structures and less than 5 percent of 1,2-vinyl structures,
• c) from 1 to 15% by weight, based on the sum of a) and b), of a low-boiling blowing agent, and,
• d) conventional additives in effective amounts, where the unfoamed beads have a structure in which the elastomer phase is dispersed in the polystyrene phase in the form of cell particles.