system
Given the following post, respond as if you're commenting on Reddit:
human
Why does the aroma of ground coffee permeate a plastic bag but not say, orange slices for example?

Nearly every workday I grind up freshly roasted coffee at home, and dump the contents into a zip loc baggie to take with me to the office. I frequently also do the same for other very aromatic things, like a fresh cut orange, or grapefruit, or a warm muffin. None of those other things radiate their own aroma from within that zip loc baggie. The coffee however, might as well leave the bag open it smells so strongly. I have been very careful about constraining the contents to the inside of the bag, going so far as to rinse the outside of the baggie just in case the smell is coming from the exterior. It is not. What gives? What else does this? Making me crazy!
gpt
Plastic is a wonderful material for containers; lightweight, easy to form, reasonably inexpensive.

What it is not is unreactive. You can get chemically inert plastics but they are more expensive and heavier, neatly removing the benefits to the packaging industry. Since most plastics are organic polymers instead of inorganic solids like metal and glass containers, they can and will react with many other substances. Small volatile molecules are capable of (slowly) migrating through common plastic films, and long-chain organic molecules (oils) will cheerfully bind to the plastic directly. This is why tomato sauce will stain your plasticwear red; lycopene is a long hydrocarbon.