A study on the extrusion of Eudragit E100 was carried out using supercritical carbon dioxide (scCO(2)) as plasticizer and foaming agent. ScCO2 modifies the rheological properties of the material in the barrel of the extruder and acts as a blowing agent during the relaxation when flowing through the die. For experiments, a single-screw extruder was modified to be able to inject scCO(2) within the extruded material. The aim is to determine a correlation between operating conditions and foam structure. The effect of three parameters was studied: the temperature in the die and in the metering zone, the screw speed, and the volumetric flow rate of CO2. An increase in temperature enhances the expansion rate and the average pore diameter and appears to be the most significant parameter. The effect of CO2 concentration is significant at small concentrations only: the higher the CO2 concentration, the lower the pore density and the higher both the pore diameter and the expansion rate. The effect of the screw speed is tricky because a variation of this speed involves a decrease of CO2 weight ratio. This study shows that the structure of the extrudates does not evolve with a coupling of screw speed increase and a subsequent CO2 weight ratio decrease.