Polymeric materials are very often used for their excellent properties, favourable prices, whether in interiors as decorative materials, tiles, furniture components or in the exterior as heat insulating materials. Their main advantages are low cost and low thermal conductivity, but there are also some disadvantages e.g. flammability, low resistance to thermal degradation and the formation of toxic volatile products. This diploma thesis deals with the analysis of volatile products resulting from thermal loading of selected polystyrene types at temperatures of 20, 40, 60, 80, 100, 120, 140, 160, 180 and 200 ° C. The polystyrene was thermally loaded and at the same time the resulting volatile products were analysed by HS-GC-MS method. The thesis characterises composition of produced volatile products, mass-volume changes and density of polystyrene resulting from polystyrene heating up. In the thermal degradation of polystyrene, the main volatile degradation product was styrene, which increased its content with increasing temperature. The number of volatile identified products is also increasing with the increasing temperature. At the temperature of 80 °C which is claimed by the manufacturer as the temperature of long-term thermal stability; toluene, ethylbenzene, xylenes, cyclopropylbenzene, α-methylstyrene, benzaldehyde and others were also identified along with styrene. Since these volatile products impose a significant risk to the health and life of humans, it is important to know how individual materials behave in thermal degradation, what degradation products are formed, and how to improve their chemical characteristics so that they become a safer material for a healthy life.