Angel food cakes are cooled upside down. Some tube pans have “feet” or “fingers” that extend off of the top rim of the pan. The “feet” are placed on a cooling rack. If the pan does not have “feet” it is customary for home bakers to place a glass soda bottle or something similar through the tube to ensure that the pan is elevated. The elevation provides sufficient air flow to the cake, so that it cools properly. If a non-stick pan or greased pan were used, the cake would fall out when inverted, leading to a collapsed cake.