Abstract: A plasticating screw and method of plasticating without thermal degradation problems. Said screw having a metering section with a helical flight disposed within and cooperating with the innerwall of a heated barrel. In particular, solid resinous material is introduced to a helical valley extending between said flight. The resinous material is heated and plasticized by said apparatus while being advanced along a helical path towards an outlet opening by the rotation of said screw. The bottom surface of the helical valley in said metering section having a plurality of geometrically shaped surfaces in side-by-side relation with at least two of said shaped surfaces being sloped. During operation, the level differential between the shaped surfaces induces a continuous tumbling, variable shear and mixing action upon the molten resin as the molten resin in the metering section flows along the helical path.