The polypropylene (PP) mono-filament is an alternative material that can be used for insulation, packaging, and polymer composite applications. In this study, PP mono-filaments were prepared by extrusion free-fall at temperatures of 190, 200, and 210 degrees C through a micro extrusion die with a diameter of 900 mu m. The free-fall speeds of the filament were controlled by a gear pump driving at speeds ranging from 12.5 to 20.0 min(-1), and the extrudates were cooled at room temperature. The PP mono-filaments were subsequently foamed by a batch foaming process with sc-CO2 as the blowing agent at foaming temperatures of 165, 170, 175 and 180 degrees C. The thermal properties and crystallinity of the prepared filaments and their foams were investigated using a DSC. The foam morphology and isotropic foam properties were characterized by SEM micrographs. The results show that the various morphologies of the PP mono-filament foams deviated from the isotropic foam behavior and had isotropic foam index values in the range of 1.1 to 2.3. In addition, the PP mono-filament that was foamed at 175 degrees C expanded in the longitudinal direction and exhibited the highest expansion ratio, but its degree of crystallinity decreased compared to the mono-filaments. PP mono-filament foam represented a narrow crystallization temperature range and crystallization time than mono-filament and tended to a faster crystalline growth.