Yes, you could put aluminum foil inside an air fryer. However, because of the forceful air, the foil has to be fastened to the meal or air fryer basket. According to Tasteofhome.com, if you don't, you run the danger of the foil falling free and flying off the appliance as your meal cooks. According to the website, users must "mold and shape" the foil to fit the air fryer's "basket" or the "meal you're cooking." According to southernliving.com, make sure to fasten the foil to the food or the basket rather than the air fryer's bottom, since doing so would obstruct the airflow and prevent the food from properly cooking.