Cake flour is used in cake-making. On the other end of the spectrum from bread flour, cake flour has a lower protein content than all-purpose. Whereas bread is supposed to be chewy, and therefore chock-full-of gluten, cake is supposed to be fluffy and tender. Gluten development is not the object, so cake flour is low in protein, usually around 9%. Pastry flour has an even lower protein content than cake flour, clocking in around 8%, and is mostly used to make things like pie crusts, biscuits, and scones—anything where you want a tender, crumbly, or flaky texture. In a pinch, feel free to swap cake or pastry flour for AP flour in recipes where tenderness is desirable (like pancakes), but not for things like flatbreads.