a volume reducing agent for processing expanded polystyrene , 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 .