Cats always want to be warm and try to find a comfortable spot – like leaves in the wild. Plastic bag might remind cats of leaves and will make a nice and cozy place for them. Also, these bags can provide insulation for cats.
Cats have very good hearing. There is a big possibility that your cat loves the crinkly sound of the plastic bag moving, and she can probably hear some sounds we can’t.
If your cat likes to sit on a plastic bag, always supervise her while doing this, because these bags can be suffocation hazards for cats. Also, make sure your cat doesn’t eat plastic, since it can get stuck in your cat’s intestines.