To provide a spongy expanded material made of a polyvinyl chloride resin useful as a packing material and a sealing material, especially for resin panel tanks, and a polyvinyl chloride resin compsn. for forming the spongy expanded material.

This compsn. contains 3-20 pts.wt. acrylonitrile/butadiene copolymer having not less than two functional groups having reactivity with an isocyanate in a molecule and having fluidity at room temp., and 50-100 pts.wt. plasticizer for 100 pts.wt. polyvinyl chloride resin. This spongy expanded material rich in water cutoff property and compression recoverability is obtd. by molding the spongy expanded material using an isocyanate compd. having not less than two isocyanate groups which are protected by a protective group capable of releasing the protection by heating in a molecule and a polyvinyl chloride resin compsn. compounded with a thermal decomposition type blowing agent.