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°C through a micro extrusion die with a diameter of 900 μm. 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-CO 2 as the blowing agent at foaming temperatures of 165, 170, 175 and 180°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°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.