Thermal analysis is a powerful combination of techniques used to characterize materials. In this chapter, three case studies were proposed to demonstrate possible applications of thermal analysis in the context of recycled plastics. By analyzing the pyrolysis of waste of recycled polyethylene, and through methodological procedures, the materials’ thermal behavior was delineated. The phase change and pyrolysis reaction enthalpy were estimated, and chemical kinetics was performed via isoconversional methods. As an auxiliary technique, X-ray powder diffraction was carried out to evaluate a biodegradable masterbatch and was established a comparison with the recycled materials in terms of their chemical structures.