Expandable polystyrene particles (I) containing a blowing agent have a diameter of 0.35-3 mm and are coated with 0.005 to less than 0.5 wt.% of a hydrophobic agent (II) that melts above 10 degrees C. (II) is a carboxylate of aluminum, zirconium or hafnium. Independent claims are included for (i) the production of (I) by treatment of expandable polystyrene particles with an aqueous solution containing 5-50 wt.% (II) or by coating the expandable polystyrene particles with solid (II) that has been adsorbed onto fine particulate silicic acid; (ii) the production of expanded polystyrene particles by foaming (I) or by coating expanded polystyrene particles with 0.005 to less than 5 wt.% (II); and (iii) expanded polystyrene particles prepared from (I).
