PURPOSE: To provide sufficient flexibility at the time of high temperature and low temperature by blending pellets kneaded with polypropylene, calcium carbonate and the like with thermoplastic synthetic resin at the specified ratio, extrusion molding by means of an extruder with specified LAD and further stretch molding at the specified ratio.

CONSTITUTION: Pellets composed of polypropylene and polyethylene kneaded with atactic, talc or calcium carbonate are blended with thermoplastic synthetic resin such as polypropylene by the blending ratio of 10-50%. A band belt extrusion molded by an extruder having the ratio of length of 30-40 times as much as the bore of a cylinder is stretch molded at least to seven times or more in its size, and a pattern such as emboss is formed thereon, if required. The stretched band belt is annealed without being embossed or after embossed by an embossing device to prevent the post-shrinkage and is wound up in the required length.