Injection molded ring fan embodiments and methods for making them. The methods influence material flow during the injection molding process such that a major portion of the materials flowing in opposite directions in the outer rings preferably flow past one another, intermix in a swirling relationship, and/or collide at an angle relative to one another. This results in better material mixing or integration of the flow fronts. In one embodiment, the thickness of the outer ring varies in different portions between adjacent fan blades.