A systematic strategy to molecularly design flexible tough hydrolyzed polymers of intrinsic microporosity (hPIM-1) films from the PIM-1 polymer is explored in this study. Flexible films can be fabricated from N-methyl-2-pyrrolidone (NMP) by appropriate hydrolysis conditions. The optimal weight ratio of NaOH/H2O/EtOH in the base-catalyzed reaction is 0.5/2/2. Because of the highly polar carboxylic acid groups, the resultant hPIM-1 has a lower water contact angle. The hPIM-1 has one-half fractional free volume compared to PIM-1 which is in good agreement with permeability. Moreover, hPIM-1 follows as the same dual-mode sorption model as PIM-1. To the best of our knowledge, this is the first ever reported flexible hPIM-1 film in the literature. (C) 2017 Wiley Periodicals, Inc.