To obtain a method for deforming a resin molded article into a specific shape by water swelling, a water responsive deforming resin to be deformed by this method, and a water responsive air permeable film for deforming vent holes corresponding to moisture quantity or humidity to perform the regulation of ventilation quantity or waterproofness.

At the time of swelling of a water swellable resin molded article, the swelling of a part of the molded article is suppressed by utilizing a difference in swelling ratio and the molded article is deformed. A water responsive deforming resin is obtained by bonding a molded article of which the swelling ratio is less than that of a resin molded article to the water swellable resin molded article. A water responsive air permeable film is obtained by bonding a film 4 of which the swelling ratio is smaller than that of a water swellable resin film 3 to the single surface of the film 3 and providing piercing vent holes 5 projected from the single surface of the film.