Why is there foil/bag over the sunvisor?

This sort of thing was normal in the part of India I visited. (India is a big country; I don’t know what the rest of it is like.) Cows went wherever they felt like going. If they felt like going in the road, drivers just had to accept that. One time, I saw a cow that kept trying to get into a restaurant until a waiter brought out a plate of food for it to eat outside.