Well, PET is probably one of the best plastics to use for just pure odor containment. It is great with the many fragrances out on the market. Fragrances are generally stored in glass, but, depending on the fragrance, is also stored in PET bottles. PET is also good with hydrogen permeability, but I don't know how that translates to odors. The best is aluminum, or metal. A lot of times when you buy an aluminized bag, like a mylar balloon or a squeeze drink container, the material is a 3 layer lamination with aluminum being the middle layer and PET or nylon being the outer layer. Of course, mylar is PET, so there is that. If you took a PET bottle and then sprayed an aluminum layer on it, and then sprayed a PU layer on top to protect the aluminum, you will get the least amount of any gas permeating through.
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