A reusable, air-permeable packaging film formed of a layer of resilient and nontoxic material is disclosed. The packaging film includes a plurality of micro-gaps distributed within a pre-selected area on the packaging film, wherein each of the micro-gaps traverses thickness of the packaging film, and wherein, in a static state, i.e., no pressure/stress exerted on the packaging film, each of the micro-gaps comprises a split upper seam portion with edge ridges demonstrated on a top surface of the packaging film and a close lower seam portion communicating with the split upper seam portion. During microwaving, the pressure can be regulated at a relatively lower vapor transferring rate through the pre-selected area.