My freezer dryer came with mylar bags. At first, I just used glass jars, but ran out and thought mylar was more like the metal lining in milk cartons and stuff. They set off metal detectors, (I tried to take freeze dried apples through TSA...)so thats why I leaned that direction. I've also bought a lot of long-term food storage items in mylar bags, like MREs, peanut butter, instant potatoes etc.
They're more prevalent in the prepper world.