Expandable styrene polymer particles which have fast cooling rates during molding are produced by suspending styrene polymer particles in an aqueous medium and impregnating a blowing agent into the particles in the presence of 0.05 to 0.4 parts of silicone surfactant per 100 parts of polymer particles. The silicone surfactant is selected from the siloxane-oxyalkylene copolymers having at least one polysiloxane block which contains mers of the general formula R2SiO, where R is selected from the group consisting of alkyl having 1 to 4 carbon atoms and halogenated alkyl having 1 to 4 carbon atoms, and at least one polyoxyalkylene block containing mers of general formula CnH2nO, where n is 2, 3 or 4, attached to said polysiloxane block and terminated by hydroxyl groups.
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