The change of porous structure of polyimide films was studied with regard to the method of processing (swelling in supercritical carbon dioxide or addition of a salt during the synthesis followed by washing the polymer film to remove that salt), conformational rigidity, presence of fluorine atoms in the repeating unit, parameters of swelling with carbon dioxide and the quantity of salt which was added during polyimide synthesis. By using atomic force microscopy, transmission electron microscopy and scanning electron microscopy in this study, it was shown that both methods of processing the polymer films allowed the formation of a porous structure whose parameters depended on the chemical structure of the polyimide and on the way to process the polymer film. (C) 2012 Elsevier B.V. All rights reserved.