Frito-Lays has introduced a new bag for their Sun-Chips that is claimed to be biodegradable. Made largely from PLA supplied by Natureworks, the bag is a pretty thin (20 mm thick - 0.0008 in) thick with six layers: PLA-print-adhesive-metal layer-PLA-PLA sealant.
My first job after all my schooling was making packaging films out of PP, so I cen relate to some of the challenges mentioned in the article. The sealant appears to be needed as the PLA must melt at too high of a temperture to allow for a quick thermoseal. And the sealant can only seal to itself, forcing the use of a fin seal rather than a lap seal.
One interesting bit of trivia I learned all those years ago is that potato chips need to be kept in the dark - you don't see any bags with windows in them as you do with corn chips. The light apparently will cause the oils in the chips to go bad.
So how can the metal layer be considered biodegradable?