You’ll need 6 pieces of heavy-duty tinfoil, each about 20 inches long. The basic idea is to use two sheets of tinfoil to create one larger one.
Lay your first piece of tinfoil, shiny side up.
Lay another piece of tin foil directly overtop that one, with the shiny side down (so the shiny sides are touching).
Fold one of the long edges over about 1/2 an inch. Press down to make it flat. Then, fold that edge again. And again. And again. Probably 4 or 5 times, fold it and press it down so it’s nice and flat. The folds will create a seal and join the two pieces together.
Gently open the sheets up, like pages of a book, and lay your now large piece of tinfoil down, shiny side up. Repeat this process two more times with the other 4 sheets, until you have 3 large sheets of tinfoil.
Next, lay one of the large sheets on top of the other (both with shiny side up) and fold each edge over about 1 inch (you can see it in the picture below). Do this twice, creating a large, double-thick sheet of tinfoil. This will be the base of your packet.