Figure 1 shows the micrographs of virgin and recycled PET fibers obtained at different magnifications. The surface morphology of the virgin fibers consists of smooth cylindrical fibers. It appears that this smooth surface is caused by the partial solidification that occurs as soon as the fiber leaves the extruder [33]. Experimental studies have reported that the viscosity of the PET polymer has a significant impact on the fiber diameter than any other process variable [34]. Therefore, different average diameters should be obtained for virgin and recycled PET (see Figure 1). In fact, virgin fibers showed a lower diameter than that obtained for recycled fibers. This is because the lower flow mass of the virgin PET at the process temperature, caused principally by the lower flow index of the raw material in comparison to the recycled material. Additionally, the surface of virgin fibers has lower defects and higher shining than those obtained for the recycled fibers.