This is a plastic bag.
Estimated persistence
≈ 10-20 years
Why it matters
Thin bags and wraps are usually polyethylene, often #2 or #4 depending on the exact type. They are cheap, strong for their weight, and easy to hand out. They are also easy to lose, which is why they show up in streets, waterways, and wildlife habitats.
Even when they degrade, they do not vanish. They tear and fragment into smaller pieces. Those pieces can be eaten by non-human animals or move through ecosystems as microplastics. The practical problem is the repeat habit of accepting disposable film for short tasks that could be handled another way.
Details
Mechanism
Thin bags and wraps are usually polyethylene film, often HDPE (#2) or LDPE (#4) depending on the product. They are strong for their weight and easy to distribute, which is why they spread so easily.
After disposal
Once loose, film plastic tears and fragments. Those pieces move through streets, waterways, soil, and habitats, where they can be eaten by animals or persist as microplastics.
Better substitutes
Reusable bags help when they are actually reused many times, so keeping them where you will remember them matters more than buying more of them. Refusing just-this-once plastic at checkout reduces the flow of new bags into your routine. At home, containers, lids, and reusable covers reduce the need for film wraps, and if you keep plastic bags for liners or messes, use what you have fully before taking new ones.