High performance thermoplastic blends based on polyethersulfone (PES) and poly(ethylene 2,6 naphthalate) (PEN) were foamed with supercritical CO2 to develop high-performance foams with improved heat deflection temperature, extended processing range, and controlled cellular morphology. The cellular morphology resulted to be strongly influenced by the initial morphology of the blend. The presence of small amount of PES as dispersed phase in PEN based blends acted as blowing agent reservoir and allowed to extend the processing temperature range for obtaining low density foams. The presence of PEN droplets in PES based systems extended the foaming temperatures towards lower values and allowed the development of a bimodal micro/nanocellular morphology at a foaming temperature 60 degrees C lower than the PES glass transition temperature. Furthermore, the presence of PEN droplets compensated for the reduced capability of the host matrix to generate a fine and diffuse porosity at low foaming temperatures. POLYM. ENG. SCI., 55:1281-1289, 2015. (c) 2015 Society of Plastics Engineers