When raw polystyrene particles containing a blowing or expanding agent are softened by heating with steam, the hollowed closed cells are formed within the particles, which expand up to 50 times their original volume.
Blocks of polystyrene are made by resoftening the expanded particles in a block mould with steam until they fuse together. The block is then cut into sheets or boards.
Shaped polystyrene products are produced either by cutting blocks with a hot wire or by direct moulding of the expanded particles in specially shaped moulds.
Extremely effective, essentially because stabilised air is such a good insulator. The thermal performance of a material is measured in terms of its resistance to the flow of heat. This thermal resistance is expressed in R-values. The higher the number, the better the insulation. The R-value of the most commonly used class (Class SL) is 1.13 for every 50mm thickness. Tus, 44mm of this class of moulded polystyrene delivers an R-value of +1.0.
Moulded polystyrene is a closed cell and cannot absorb water. During the process of moulding a block, tiny channels are formed between the polystyrene particles. If the material is immersed in water, these tiny channels can be filled with water. After immersion for more than 360 days, there may be up to 6% water content by volume which has entered the channels. Even under such an adverse and rare condition of prolonged saturation, there is a very little adverse effect on moulded polystyrene. It maintains its shape, size, structure and physical appearance. The ability of moulded polystyrene to resist the adverse effects of moisture is exemplified by its widespread use in floats, marinas and other applications, which involve full or partial submergence in water for prolonged periods of time.