It transforms raw expandable polystyrene (EPS) beads into uniformly expanded beads at precise target densities-typically ranging from 7g/L to 45g/L (7–45 kg/m³)-through a closed‑vessel steam expansion process. The expanded beads are then aged, dried, and molded into blocks or shaped products for building insulation, protective packaging, and custom foam components.

Unlike continuous pre‑expanders, batch pre‑expanders operate in cycles-weighing a specific quantity of raw beads, expanding them, and discharging before reloading the next batch. This allows for precise per‑batch density control and is widely recognized as the preferred technology for applications where density consistency is critical.