Physical foaming was conducted in a high-pressure stainless steel autoclave. Round plate samples of neat PLA and PLA/CNF nanocomposites were prepared using a compression mold with a diameter of 10 mm and thickness of 1 mm. After weighing, each sample was placed on a sample holder inside the autoclave. The autoclave was filled with a blowing agent, compressed CO2, for a few seconds and then pressurized with the blowing agent and heated to the solubilization temperature. The pressure of the blowing agent at this temperature was adjusted to the desired saturation pressure (20 MPa). A solubilization time of about 1 h was maintained to ensure equilibrium. After saturation, the pressure was quenched to atmospheric pressure within 3 s, and the samples were taken out. The foam structure was allowed to grow fully during rapid depressurization.