There are two things that make angel food cake so light and airy - whipped egg whites and cake flour. Much of the structure of this cake comes from the stabilized egg whites. It's important to properly whip the egg whtes because those whipped egg whites give the cake its light and fluffy texture. The other thing that helps to make the cake light is using cake flour. Cake flour helps to give the cake its softer texture because cake flour is a soft white flour that is lower in protein, which helps to make the cake tender.