To improve the surface smoothness, flexibility, transparency, moist heat resistance and hot water resistance by dissolving a polyvinyl alcohol polymer in a mixture of water and a water-soluble organic solvent and bringing the solution into contact with a vapor-phase water to form a gel.

A polyvinyl alcohol polymer containing structural units of formula I (wherein R1 is H or a monovalent hydrocarbon group; and R2 and R3 are each a monovalent hydrocarbon group, or R2 and R3 or R1, R2 and R3 are combined together to form a ring with a carbon atom bound thereto) in a mole fraction of 0.05 to 0.50 and having a block character, defined by the formula A {wherein [OH,VES] is the mole fraction of methylene carbon atoms lying between a methine carbon atom to which hydroxyl groups are combined and a methine carbon atom to which acyloxy groups are combined; [OH] is the mole fraction of vinyl alcohol; and [VES] is the mole fraction of the vinyl ester units of formula I}, of at most 0.6 and a viscosity-average degree of polymerization of at least 300 is dissolved in a mixture of a water-soluble organic solvent and water, and the solution is brought into contact with a vapor-phase water at 0-100°C and a relative humidity of 5-10% to form a gel.