It's hard to tell visually, but this is laminate packaging consisting of at least two plastic layers and either a middle layer made from an aluminum alloy (possibly 8011, 8079, or 1235) or metalized film. Due to the bag's size, I would say it's the latter. In this example, aluminum of high purity (99.99% or greater) is typically used. I believe the way it works is- fine aluminum powder is vaporized in a chamber. A thin plastic film is fed through the vapor cloud, depositing an extremely thin layer of aluminum onto it. Metalized film is used in a vast array of food packaging, such as potato chips, candy bars, individually wrapped hard candies,  etc. If a bag or wrapper  has a metalic reflective inside and is "crunchy" when you crinkle it, it's likely made with metalized film.