Without aluminum outer wrapping, it would melt to the food. Aluminum outer shell acts as a buffer from the direct heat, and holds moister in which acts as a melt retardant. As far as poison leaching into the food being cooked, well it would be such a small amount that it would not make a difference. You would get more plastic toxic leaching in a gallon of milk then you would in a dozen slabs of ribs wrapped in plastic than aluminum foil and baked. I have made full slabs of ribs using the plastic wrap than aluminum foil method many times over the years, and I have yet to have one come out with any taste of plastic, in fact, they are better tasting and more tender then the ribs I have cooked without the plastic wrap. Warnings are on the box for a reason, to prevent the inexperienced from making bad mistakes and ruining their food. Baking fish in the plastic/aluminum wrap method, well first off, you'll be baking at temps that would not cause any melting of the plastic, and the length of time baking is surely not long enough either to melt the plastic. Remember, the moisture will prevent the plastic from melting. Maybe a compromise: use parchment paper. Fold a large enough piece in half, place the fish on one half with seasonings and a lemon slice, fold edges over, wrap in foil, place it on a cookie sheet, and bake as you always do. You find no threat of leaching, but really good tasting moist fish. Have fun! Merry Christmas!