PURPOSE: To produce the titled material having fine orientated pores, by molding a mixture of specified PE and paraffin into a plate, rolling the plate and removing the paraffin by extraction.

CONSTITUTION: 1pt.wt. powdered PE of a weight-average MW of 2×105W5×105 is mixed with 1W10pts.wt. solid or liquid paraffin and the mixture is heated, after deaeration, to a temperature ≥ the m.p. of the PE to dissolve it in the paraffin. The obtained thick solution is homogenized by kneading in a screw extruder, a mixer, or the like and extruded through a die slit into a plate. This plate is solidified by cooling to a temperature ≤ the solidifying point of the PE, and rolled at 60W120°C by rollers to a thickness which is 1/3W1/40 time the initial thickness. This rolled plate is immersed in a volatile organic solvent to remove the paraffin by extraction.

EFFECT: It is possible to form pores of a size which is about one tenth that of the conventional. The control of a pore size is easy, and a porosity of 70% at maximum can be attained.