With a world-wide consumption of 10.5 million tonnes in 2001 polystyrene is counted amongst the quantitatively most important thermoplastics and continues to be ranked in fourth place after PE, PP and PVC. Also in recent years on the average the dynamic development of consumption was a little greater than that of the gross domestic products of the corresponding countries and it is generally expected that this development will continue. General economic cycles as well as inter-polymer substitution processes (PP, PET, ABS) affect this development in different time frames.