This set contains two 25x20cm sheets of white 0.5mm thick Polystyrene. The product consists of High Impact Polystyrene Sheet (HIPS).
Plasticard (or Sheet Styrene) is an amazingly versatile material for modeling and converting. It is dense polystyrene and is essentially the same type of plastic as you find in many plastic kits. It works with cyanoacrylate glue as well as polystyrene glue.