No one is going to put¬† coals straight onto the tobacco, unless you are smoking¬† the very strong, unflavoured Iranian tobacco.
Some people put on a wire mesh instead of using aluminum, but it doesn’t¬† keep the coals as hot, and the heat inside the tobacco bowl well. For that aluminum¬† foil is the best¬† bet.
I’ve tried the very thick aluminum foil , but it burns the tobacco too much and of course re-using it is impossible, since with any foil, the¬† protective layer burns after one time any ways.
Best is to buy the ready cut in a circle thin foil and make sure that you put the shiny part down toward the coals¬† underneath so that it reflects the heat down toward the coals instead of taking the heat energy and lifting it away from your tobacco.