Abstract: The disclosure relates to a folding container or carton having sidewall panels with at least one of the panels containing a reinforcing rib which extends vertically when the carton is erected. The rib projects toward the interior of the carton when the carton is erected. The provisions of the rib in a side panel of the carton increases the stiffness of the panel and prevent it from buckling in response to the pressure exerted on the panel by the material or goods contained within the carton. The reinforcing rib also acts as a column which increases the ability of the carton to carry the load of one or more cartons stacked upon another. The disclosure also relates to a jig or fixture which facilitates the erection of sidewall panels having reinforcing ribs by maintaining the rib in its erected form during the setting up of the carton and also to support the sidewall panels of the carton from deflecting or bulging when the carton is being filled with dense bulky material.