The organic polymeric material having a softening point of lower than about 80??? C. is preferably selected from polyolefins such as polyethylene and polypropylene; ethylene copolymers such as an ethylenevinyl acetate copolymer, the saponification product thereof, an ethylene-acrylic acid ester copolymer and the saponification product thereof; polyvinyl chloride; vinyl chloride copolymers such as