The satellite dish companies make a trade-off: they paint the surface of the dishes with a thick, durable coating to prevent them from rusting. However, that also insulates electricity and it attenuates the signal from the satellite a little as well as blurring the focus of it onto the receiving antenna. Most of the time this is not a problem. But when the sun passes right behind the satellite, its electromagnetic energy output overwhelms the already weakened signal.
The solution, therefore, is to apply a coating that is free of an insulating barrier and offers nice sharp focus of the electromagnetic energy rays onto the receiving antenna. But what to use?
Simple aluminum foil! It conducts electricity and its shiny surface helps focus the the energy much better.