A volume reducing agent for processing expanded polystyrene (EPS), containing 65-97 wt % of a first plasticizer having a solubility parameter less than the solubility parameter of the polystyrene; and 3-35 wt % of a second plasticizer having a solubility parameter higher than the solubility parameter of the polystyrene. The volume reducing agent is in a liquid state, has a Ferdor solubility parameter close to that of the polystyrene to be processed in the mixed state and transfers the resulting materials having reduced volume into gel-type products to be floated and easily separated to yield a high quality output of recycled expanded polystyrene (FPS).