A range of thermal analytical techniques have been used to characterize PVB obtained from various manufacturers and recycled material recovered from glass recycling units. C-13 NMR spectroscopy was used to confirm that PVB is a random terpolymer containing butyral and hydroxyl side groups with a small amount of acetate units. Little variation in chemical composition was observed between the grades studied. The PVB also contained between 20 and 25 wt.% of plasticizers and GC mass spectroscopy has been used to determine that the dominant plasticizer was dibutyl sebacate. A more convenient method to determining the amount present, however, was differential scanning calorimetry since PVB being an amorphous rubber its glass transition temperature, T-g, varied with plasticizer content. Most recycled PVB samples had similar T-g's but these could be adjusted by addition of further amounts of dibutyl sebacate. PVB decomposed by side group elimination above 260 degreesC. Butyraldehyde, butenal, water, and acetic acid were the major components from these elimination reactions, but benzene and other aromatic products were observed from the decomposition of polyene residues. Below 260 degreesC the change in mass was attributed to plasticizer loss by the evaporation of dibutyl sebacate from the PVB matrix. It was concluded that recycled and blended grades of PVB could be re-used as a laminating agent for glass and that PVB should be recycled rather than placed in landfill.