A method of manufacturing bulked continuous carpet filament, in various embodiments, comprises: (A) providing an expanded surface area extruder; (B) providing a spinning machine having an inlet that is operatively coupled to an expanded surface area extruder outlet; (C) using a pressure regulation system to reduce the pressure within the expanded surface area extruder; (D) passing a plurality of flakes comprising recycled PET through the expanded surface area extruder to at least partially melt the plurality of flakes to form a polymer melt; and (E) substantially immediately after passing the plurality of flakes through the expanded surface area extruder, using the spinning machine to form the polymer melt into bulked continuous carpet filament. In some embodiments, the method may include passing the plurality of flakes comprising recycled PET through a PET crystallizer prior to extrusion.