Store bought baking powder is typically double acting. A second acid in the baking powder reacts when its heated in the oven. If youre looking for a good double acting baking powder, I recommend the Rumford brand. Its aluminum free, non GMO, gluten free and contains no preservatives or additives. It does contain corn starch, however, so it wont work for people with corn allergies. Most grocery stores carry it. If you dont see it in the baking section, check the natural foods section. Its in a red can. See Also What to Do If You Add Too Much Baking Powder.