Angel food cake is part of a group of cakes called foam cakes. Foam cakes are composed of flour, sugar, eggs, and flavoring. They contain no chemical leavening agents. Chiffon cake falls into this category, as does tres leches cake (which is essentially a chiffon cake soaked in three milks). One key way that chiffon cakes differ from angel food cakes is that chiffon has butter in the batter. See my post on angel food cake vs. chiffon cake for more on this subject.