The importance of recovering and valorising the residues generated by industrialized societies is mainly due to the environmental impact that such residues may cause. In this connection, scrap tires constitute a major source of pollution. In the recent years large amounts of scrap tires have been recycled in order to recover the metals contained in this residue. Tires have also been grinded and the small particles produced have found different applications. In addition to metals and rubber particles, reinforcing fibers are also produced in the recycling process of scrap tires. As a previous step for the valorisation of this third constituent of waste tires, a characterization of such fibers is strongly recommended. Thermal analysis techniques make it possible to identify the fibers through the thermal transitions that may take place. Usually, such transitions result mainly in cotton and rayon. Furthermore, the combination of pyrolysis, gas chromatography and mass spectrometry techniques corroborates the identification of several compounds derived from the decomposition of the fibers as well as some materials used in the preparation of tires.