Prefoamed expanded polystyrene

Another cavity wall and foam technique is done by use of prefoamed EPS particles. The cavity between the two faces (walls) can be completely filled with the prefoamed expanded polystyrene (EPS) particles and then foamed by applying steam. 

Expandable polystyrene beads are often molded in two separate steps (1) Preexpansion or prefoaming of the expandable beads by heat, and (2) further expansion and fusion of the preexpanded beads by heat in the enclosed space of a shaping mold. 

Plastics manufactured from prefoamed (pre-expanded) granules such as polystyrene are also composite systems according to the proposed classification. 

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