I remember when I was on my cousin's house and saw foil wrapped on their ceiling and walls. I was really wondering what was the purpose of it. Out of my curiosity, I googled it and found out that it was a foil insulation. The purpose of it was to stop the movement of heat. It acts as a radiant barrier both in the summer and winter. I also read that double bubble insulation which is also a foil insulation is a really good barrier in heat and cold season. I just never thought that a foil has such a useful and amazing function.