Difference between two sides of polypropylene film

Does the subject want to ask, "Does pp film have two sides?" ? No. PP filter membrane is isotropic, which can intercept solid particles above the rated pore size regardless of the front and back. The domestic filter membrane has no front and back, because the microporous filter membrane is symmetrical and has the same effect on both sides. The reason for the smooth cleaning is that the domestic filter membrane is made of coating liquid on the glass plate, and the side attached to the glass is smooth.