The thermal bonding behavior of different grades of polypropylene was studied in this research. Initial bonding studies were done with polypropylene films of different grades of polymer with varying morphology, and the studies were extended to polypropylene fibers. Polypropylene fibers manufactured with different cross-sections, deniers, polymer melt-flow rates, and different processing conditions were bonded under various conditions. The effect of film structure, properties, and bonding conditions on the bonding efficiency was studied by comparing the tensile strength of bonded films. Thermal bonding was carried for a range of temperatures covering poor, optimum, and over bonding. Changes taking place to the polymer in bond point and the original surface were analyzed using the SEM. Higher bond strength was observed in the vicinity of melting temperature and the strength reduced with a further increase in bonding temperature. The frequent failure point was observed at the bond edge crossover points where film undergoes maximum thickness transition. Lower pressure and shorter time were found to be appropriate for bonding. Films with lower orientation formed better bonds. The optimum bond strength and the optimum bonding temperature observed were different for different polymers. Fiber bond strength results were similar to the results observed in the case of films with respect to the bonding temperatures Studied. (C) 2008 Wiley Periodicals, Inc. J Appl Polym Sci 110: 3047-3058, 2008