Operating temperature of polystyrene from -200 to +85 C. Water absorption foam Unlike other materials Styrofoam is not hygroscopic. Even under water, it absorbs little moisture. Since the walls of the cells are impermeable to water, it can leak out only through the channels between the individual associated with each other between the cells. Water absorption is measured by the standard method. Test samples are squares with the surface of 200×200 mm and the corresponding thickness, immersed completely in water.

The water absorption is virtually independent of the bulk density. It is reached after 24 hours up to 2-3% in terms of volume. Water absorption during curing under water not only plays a significant role for most of the material and is of interest only in special situations. Since polystyrene does not dissolve or swells in water, and because no coherent structure containing air cells, almost does not absorb water. The water in the liquid phase can, in principle, to penetrate the labyrinth between the granules fused together, mainly due to capillary action, but can always leave the maze, without affecting long-term adverse effects on the mechanical strength, size, physical appearance or the insulating properties of the material. In addition, by increasing the degree of fusion between the granules through optimization of molding, the capture of water is minimized. Water vapor phase able to penetrate, and polystyrene, although at a density of 30 kg/m3 and above, the rate of displacement less than 1% compared to the speed of movement of water through the stable layer of air of the same thickness.