A METHOD FOR PRODUCING A COMPOSITE POLYMERIC FIBER WHICH INVOLVES INTRODUCING A FIRST POLYMER HAVING FIBER FORMING PROPERTIES INTO A FIRST INLET ZONE, INTRODUCING A SECOND POLYMER HAVING FIBER FORMING PROPERTIES INTO A SECOND INLET ZONE, SAID FIRST AND SECOND POLYMERS HAVING INHERENTLY POOR ADHERENT PROPERTIES RELATIVE TO EACH OTHER, CAUSING ALL OF SAID FIRST AND SECOND POLYMERS EXITING FROM SAID FIRST AND SECOND INLET ZONES TO FLOW INTO A MIXING ZONE THAT DOES NOT COMMUNICATE WITH ANY OTHER INLET ZONES, SAID MIXING ZONE BEING AT LEAST PARTIALLY FILLED WITH A PACKING MATERIAL HAVING A DIAMETER OF ABOUT 0.2 MM9 TO 2 MM. AND WHICH FORMS A BED AT LEAST 5 MM. THICK AND CAUSING ALL OF THE POLYMERS FLOWING THROUGH SAID PACKED MIXING ZONE TO THEREAFTER BE EXTRUDED THROUGH A SINGLE SPINNING HOLE AS A SINGLE COMPOSITE FIBER, THE SINGLE COMPOSITE FIBER EXITING FROM SAID SINGLE SPINNING HOLE HAVING A JAGGED BOUNDARY INTERFACE FOR THE COMPONENT POLYMERS, SAID JAGGED BOUNDARY INTERFACE BEING MINUTELY AND IRREGULARLY COMPLICATED WHEN VIEWED FROM BOTH THE TRANSVERSE AND LONGITUDINAL AXES OF THE FILAMENT.