This thesis entitled „Volatile products of thermal degradation of select type of thermoisolating materials“ brings knowledge about volatile products of thermo degradation of selected type of polystyrene analyzed by gas chromatography method with mass spectrometry. It is focused on analysis of polystyrene ceiling plates expanded and extruded polystyrene. Target of thesis is analysis of taken volatile products of thermal decomposition of two selected types of polystyrene ceiling plates, specifically quantitative analysis focused on styrene. Samples were submitted to thermal decomposition in experimental lab at temperatures 150 °C and 300 °C, while we are focusing on analysis of quantity of styrene as dominant thermodegradating product and we are also focusing on description of behavior of polystyrene at mentioned temperatures.