Plastics are among materials that are diverse with the possibility of versatile use in industry. They are all more or less flammable materials, so it is also necessary to deal with them from the point of view of fire protection and safety. The diploma thesis focuses on the evaluation of plastics used in construction by methods of thermal analysis. Selected plastics such as polyethylene, polycarbonate, polymethylmethacrylate, polypropylene were tested in the experimental part by thermogravimetric analysis and differential scanning calorimetry. Sample testing has been carried out in accordance with STN EN ISO 11358 and STN EN ISO 11357-1. The introductory part provides basic information on plastics, and in particular their properties, their use in the construction industry, fire behavior. Another part is devoted to the characteristics of selected types of plastics and to the description of individual methods of thermal analysis. The main part of the diploma thesis is focused on the evaluation of the results of the tested plastics by thermogravimetric analysis and differential scanning calorimetry. The highest thermal stability achieved a polycarbonate sample at which the weight loss was recorded at 367 °C. Polypropylene had the lowest thermal stability, the weight decrease was already at 234 °C. DSC analysis revealed a significant difference in samples of polymethyl methacrylate, which as the only significant endotermic effects.