Supercritical CO2 (scCO(2)) is used as a medium for foaming amorphous polymers. A study of the solubility of supercritical CO2 in several amorphous polymers (PS and PMMA) and blends is performed, followed by an investigation of the foaming behavior of the polymer-gas systems. Nano-structuring triblock copolymers (styrene-co-butadiene-co-methylmethacrylate SBM and methylmethacrylate-co-butylacrylate-co-methylmethacrylate MAM) were blended as additives to PS or PMMA by extrusion. The addition of these triblock copolymers results in an important weight gain ratio of gas in a wide range of temperatures (from 25 to 80 degrees C), relating this weight gain ratio to the foaming behavior of the blends (CO2 is preferentially located in the micro or nano-domains issued from the structuration of the block copolymer). Foaming is carried out in a batch one-step scCO(2) process, keeping constant the saturation pressure and depressurization rate (300 bar and 60 bar/min, respectively). Influence of saturation temperature (25-85 degrees C) on the final porous structure is shown. In spite of the influence of the terpolymer on the weight gain ratio, the structuration is believed to provide a good control of microcellular foams in PS and PMMA.