A method of decreasing the bulge of gable top cartons by evaluating and modifying top sealing heat patterns. Cartons are formed, dye stained and the quality of the seal evaluated for heat damage and top seal quality. The heating pattern is adjusted as required, and the resulting heat seal is reevaluated to determine if further adjustments are required, so that the resulting cartons can achieve a near air-tight condition in the headspace of the carton to thereby resist bulging.