As a result of the many voids in it. It is characterized by being lightweight, low in thermal conductivity, and does not leak water, preventing it from reaching the casting, which protects it from corrosion and cracking. It can be easily applied because it comes in the form of boards placed next to each other, so it is characterized by being a good insulator. It has many densities, so the higher the density, the greater the hardness. Its types: Extruded Polystyrene Foam: This type is manufactured by melting polystyrene granules in a special melting device, with the necessity of a blowing agent. It is also characterized by its strong ability to resist heat, being homogeneous, lightweight, resistant to pressure, and of high density. Low price, so it has been widely used in the recent period due to its great importance in protecting surfaces. Price: 35