A quantitative technique has been developed to measure the extent of fusion between expanded beads in molded polystyrene foams. Experiments were conducted with ASTM D638 tensile test specimens that were molded under conditions to produce various levels of bead fusion in the foam. The tensile properties of the foam for various levels of bead fusion were measured according to ASTM D638 standards. The fracture surfaces of the tensile specimens were analysed by quantitative image analysis techniques to measure the degree of bead fusion in the sample. This technique was then used on a commercial pattern to map the variations in bead fusion at numerous locations in the molded part. The results indicate that there is a good correlation between the tensile properties and the measured bead fusion. Significant variations in bead fusion may be present in a single molded part. (C) 2003 Kluwer Academic Publishers.