Microcellular Foaming Extrusion uses film-processing technology that forms homogenous microscale bubbles of several to tens of μm inside the film through highpressure injection of polymer resin dispersed and discharged from the screw through an inert gas from the die gap. Gases used at this time include nitrogen, carbon dioxide, helium, and argon. The properties influencing the bubbles’ growth rate and physical properties are greatly affected by the initial bubble radius, resin melt viscosity, line speed, bubble injection pressure, and die gap. In particular, if the foaming agent has a large amount of decomposition heat and low melt viscosity, the temperature of the foam decomposition part is high, which may cause bubbles to be much larger.