Plastic foam with a nanoscale cell structure was prepared from poly(ether ether ketone) (PEEK)/para-diamine poly(ether imide) (p-PEI) as well as PEEK/metadiamine poly(ether imide) (m-PEI) blends by a temperature quench foaming method with CO2. The difference in chemical configuration between m- and p-PEI gave rise to a prominent change in the higher order blend morphology and cell structure of the respective foams. The bubble nucleation site and bubble size were controlled by templating the morphology of the PEEK/p-PEI blend, which shows an immiscible and unique strip-patterned crystalline morphology. The properties influenced by the immiscibility of the PEEK/p-PEI blend were investigated using SEM, thermal analysis and rheology and compared with the properties of the miscible PEEK/m-PEI blend. The bubble size and location were highly controlled in the PEI disperse domain that was aligned between the PEEK crystalline layers in the PEEK/p-PEI blend. POLYM. ENG. SO., 50:2408-2416, 2010. (C) 2010 Society of Plastics Engineers