The work deals with the effect of polystyrene modification on the formation of degradation products under thermal stress. A sample of the material is expanded polystyrene EPS 70F, 100F, and EPS Gray Wall by Isover, which are used as alternatives to the contact thermal insulation system. Polystyrene samples were thermally loaded at a temperature range of 20 ° C to 200 ° C in a Head-Space. Changes in volume, density, thermal stability, polymer chain stability, changes and presence of functional groups, formation of degradation products were observed. Modification of polystyrene with graphite brings with it increased thermal stability as well as better thermal insulation properties, on the other hand it brings more change in density, qualitatively and quantitatively more volatile products. Chapter results of volatile products is extended to possible technical solution to eliminate evolution of degradation products in the environment by added unbounded graphite.