Polymer foams with controlled and templated pore size have been obtained for the first time by CO2 gas dissolution foaming from poly(methyl methacrylate) (PMMA) films. This kind of materials, with a variable porous structure, mimic some high-performance natural materials and could present significant interest in many applications. However, up to now their controlled fabrication has not been successfully achieved. Herein, we present a method to achieve a fine control in the production of such materials. Thermal in situ synthesis of ZnO nanoparticles from Zn(OAc)(2) was proposed to obtain PMMA nanocomposites, in which the ZnO nanoparticles induce heterogeneous nucleation that leads to formation of pores with size below the micron, upon CO2 foaming. Starting from templated solid PMMA samples with well-differentiated regions, presenting or not ZnO nanoparticles, it was possible to obtain PMMA-based foams with well-defined areas of different pore sizes. (C) 2017 Elsevier Ltd. All rights reserved.