Disclosed is a process for production of expanded polystyrene using D-limonene as a plasticizer, which allows reducing the amount of pentane in the process, yet allows generating beads with similar cell size as if greater quantities of pentane had been used. Pentane is an organic solvent with toxicity associated with organic solvents. After forming beads, they are melted in a mold to form a variety of products, or they can be extruded in a process where limonene is used instead of or in addition to other blowing agents.