system
Given the following post, respond as if you're commenting on Reddit:
human
Why are water bottles always #1 plastic, milk jugs always #2, and yogurt/margarine containers always #5?
gpt
I am a packaging engineer. The numbers refer to different types of plastics which all have different properties - strength, barrier to oxygen or moisture vapor, how it reacts to temp extremes etc. There are a variety of reasons the packaging is chosen including how the product will be filled, how it will be stored, consumer needs and product compatibility with the package. Example PP holds up well to heat which is why it is used for hot fill applications, microwave trays and sealant films for steam able veggie bags. Also you might see "other" which can mean either it is a coex (think a sandwich of different plastics to take advantage of all the features of the different layers) or that the plastic doesn't have a number assigned. Example of a coex "other" is ketchup bottles use a coex containing EVOH which is an oxygen barrier and keeps your ketchup from oxidizing and turning brown, since EVOH dissolves in water it gets sandwiched between PET. (Sorry for typos on phone)