Key Takeaway
To keep food fresh in a Mylar bag, press out excess air, add an oxygen absorber only when appropriate for dry food, clean and flatten the seal area, then make a continuous heat seal above the zipper; vacuum sealing works only with equipment compatible with smooth Mylar. Keep crumbs, powder, and wrinkles out of the seam, follow the bag maker's temperature guidance, let the seal cool, and inspect it for gaps. A household iron, flat iron, or impulse sealer can work when used correctly. Label the contents and date, store the bag in a cool, dry, dark place, and do not treat the zipper alone as an airtight long-term seal.
