an air ring with increased - control over the gauge uniformity of blown plastic film in a film extrusion device . the air ring includes a generally annular plenum , an annular orifice for discharging cooling air against an extruded plastic tube passing through the air ring , and a flow path for cooling air between the plenum and the annular orifice . the air flow path is segmented along a circumference of the annular plenum , the segments including a material with high heat conductivity and guiding the air from the annular plenum to the orifice . heating elements are provided for individually and selectively heating the segments of the air flow path such that the temperature of the cooling air discharge against the extruded plastic tube can be locally varied .