hollow injection molded article made of plastic material , esp . preform for blow molding a container , with a wall extending along axis , which is composed of a layer of variable thickness , being remarkable in that longitudinal ribs are provided in said axis direction , wherein the wall has a tooth profile of periodic nature varying periodically between a minimum and a maximum threshold value which is determined by a typical injection molding length for said plastic material and / or characteristic ratio . a method of manufacturing thereof by injection molding comprising forming inner and outer preforms with formation of an integrated composite preform , and apparatus for this purpose .