The seitan roast needs to be wrapped to keep it moist and not dry out during the initial baking. There have been studies that have shown that aluminum from foil (and cookware) can leach into food when cooked at high temperatures. I prefer to minimize my exposure to aluminum and one way to do that is by creating a protective barrier using a layer of parchment paper between the food and aluminum foil. This article provides more information about food safety and using aluminum foil.