One of the most important characteristics of Expanded Polystyrene, or EPS, is it’s ability to be molded into custom shapes.  Raw material, referred to as “expandable polystyrene beads” have to be pre-expanded in order to prep them for molding.  The expandable polystyrene contains a small amount of pentane, and when heated by steam, this pentane causes the beads to expand to many times their original size.  This material is then allowed to cool and age until it becomes a stable bead, ready to be molded into a foam cooler.  These beads are then injected into an aluminum mold, which allows steam to enter through small vents and reheat the beads.  This causes the beads to expand once again and fuse into a single shape, which the EPS retains even after cooling.  The process is known as thermoforming, and the result is a lightweight, durable, and well-insulated shipping container.