polystyrene is a thermoplastic which means that it is a plastic that can be melted and molded into any shape. So basically, polystyrene is a plastic, though it can be molded when heated whereas normal plastics just melt in contact with heat.
Rigid polystyrene plastic is a closed cell of light weight, rigid & foam plastic that is derived from petroleum and natural gas by products. It is hard plastic in one word. This is used to make...