PURPOSE: To an aqueous solution of polyvinyl alcohol is added vinyl monomers and they are reacted, then the acetalization is conducted in the presence of a plsticizer and an auxiliary foaming agent to produce title porous material with high flexibility and durability.

CONSTITUTION: Vinyl monomers are added to an aqueous solution of polyvinyl alcohol in an amount of 0.5W50 wt% based on the polyvinyl alcohol and these monomers are polymerized in the presence of a polymerization initiator. Then, 50W200 wt%, based on the polyvinyl alcohol, of a plasticizer, an auxiliary foaming agent, formaldehyde, an acid and aldehydes of two or more carbon atoms in an amount of 0.05W0.5 time molar quantity of formaldehyde are added and the acetalization reaction is effected. The polyvinyl acetate used is, e.g., a partially or wholly saporified polyvinyl acetate of 500W3000 polymerization degree or their mixture, which is dissolved in 10W25 wt%, based on the polyvinyl alcohol, of water