The process comprises blending 100 parts by weight of a polyolefin resin with 50 to 500 parts by weight of barium sulfate preferably having an average particle diameter of 0.1 to 7 mu m melting the resulting resin composition and forming it into a film, and then stretching the film at least uniaxially by a factor of 1.5 to 7. The polyolefin resin preferably has a melt index of 0.5 to 7 and a density of 0.915 to 0.935; more preferably, it is a linear low-density resin having a melt index of 0.5 to 8.5 and a density of 0.915 to 0.935. As the linear low-density polyethylene resin, a copolymer of ethylene and hexene and/or octene is particularly preferred.
