Asymmetric and nanostructured polystyrene‐block‐poly(2‐vinyl pyridine)‐block‐poly(ethylene oxide) (PS‐b‐P2VP‐b‐PEO or SVEO, S:V:EO ≈ 56:34:10, 79.5 kg mol–1) thick films blended with 20 wt% of a short PS homopolymer (hPS, 10.5 kg mol–1) are achieved by combining the non‐solvent induced phase separation (NIPS) process with a solvent vapor annealing (SVA) treatment. Here, the NIPS step allows for the formation of a highly‐permeable sponge‐like substructure topped by a dense thin layer exhibiting poorly‐ordered nanopores while the subsequent SVA treatment enables to reconstruct the material top surface into a porous monolayer of well‐ordered hexagonal perforated lamellae (HPL). This optimized film architecture generated by NIPS‐SVA shows a water permeability of 860 L h–1 m–2 bar–1, which is roughly two times higher than the flux measured through NIPS made PS‐b‐P2VP‐b‐PEO/hPS materials having poorly‐ordered nanopores. The post‐SVA treatment is also revealed as a powerful tool to tailor the thickness of the nanostructure formed within the blended material because monoliths entirely composed of a HPL phase are produced by increasing the time of exposure to a chloroform stream. The water flux of such PS‐b‐P2VP‐b‐PEO/hPS monoliths is found to be an order of magnitude lower than that of their asymmetric film homologues. [ABSTRACT FROM AUTHOR]