You probably have a bag of flour in your pantry. And it's probably all-purpose, the workhorse of baking. But there are plenty of other, more specialized flours out there, and even if you're just starting to dabble in baking, it will help to have a basic understanding of flour varieties.
The biggest difference to consider is protein content, which is often referred to in percentages. (Unfortunately, you won't find this listed on most bags of flour - sometimes it's on the manufacturer's website - but that's where we come in.) When water interacts with the proteins in your flour, it forms elastic sheets of gluten, giving baked goods the ability to rise and the stability to stay that way. So, more protein means more gluten will be formed, and the amount of structure and chew you're after will affect what flour you use.
Here's a rundown of the major types:
All-purpose: The jack of all trades, hence the name. This versatile staple is what you'll be pulling out most times you want to make almost anything: cookies, cakes, muffins, brownies, and even some breads and pizza dough. So if you're going to keep one type of flour in your pantry, this is it. The brand you use does make a difference to a certain extent, since protein content can vary from 10 to 12 percent. (Among the major available brands, Pillsbury and Gold Medal are on the low end, with King Arthur Flour at the high end.)
Whole wheat: As the name indicates, it's made from the entire wheat kernel, including the bran (protective outer layer), endosperm (the starchy food for the seed that surrounds it, used in white flour) and germ (the seed). Its protein content is 13 to 14 percent. The fat in the wheat germ can go rancid, which is why it should be stored in the refrigerator or freezer. Whole-wheat flour will give your baked goods a nuttier flavor, darker color and heartier texture. I like it in muffins, quick breads and rustic yeasted loaves.
In recipes calling for all-purpose, you can typically substitute one-third to one-half whole-wheat flour without altering the result too much, although breads can be more problematic since the bran can cut through the gluten strands. If you want to go higher than that, you may need to start adding more liquid or seek out a recipe designed specifically for whole-wheat flour. White whole-wheat flour is milder in flavor and lighter in color, making it a safer bet for large-scale substitutions.
Bread: Best for bread (obviously) and other baked goods that use yeast. The higher protein content - about 12 to 14 percent - helps create more gluten, which gives bread its characteristic chew. That stretch is what allows a dough to rise without collapsing under the slow-acting power of yeast. When making more delicate baked goods such as cake or cookies, use bread flour in place of all-purpose only at your peril; the swap will probably cause whatever you are baking to come out tough and dense.
High gluten: Similar to bread flour, but with a slightly higher protein content (14 percent). This is mostly available online and probably not worth it if you are a typical home baker. We found in the course of testing bagel recipes that bread flour performed just as well.
Cake: Many of your cake recipes will call for all-purpose flour, but there are times when you might find yourself reaching for cake flour. Its low protein content (6 to 8 percent) and very smooth, fine consistency give baked goods a tender texture and high rise. Think angel food cake, chiffon cake and biscuits. If you don't want a separate box, you can get away with using a lower-protein all-purpose flour with similar, if not identical, results. You may have seen a suggestion that you can approximate cake flour by starting with 1 cup of all-purpose, removing 2 tablespoons of flour and then adding 2 tablespoons of cornstarch to replace it, but Stella Parks (a.k.a. Brave Tart) over at Serious Eats makes a compelling argument for how the extra starch can absorb too much moisture and make your cake dense and heavy.
Pastry: Made with the same kind of softer wheat that gives cake flour its silky feel, pastry flour has a protein content (around 9 percent) that falls between cake and all-purpose. It's not something even a relatively avid baker will need very often, although some people swear by it for delicate, flaky pie crusts. Also available in whole wheat, which is the version most of The Washington Post's recipes use when specifying pastry flour.
Self-rising: This is lower-protein (around 8 to 10 percent) all-purpose flour with salt and baking powder mixed in. White Lily, often called for in Southern biscuit recipes, is one of the better-known brands. In lieu of self-rising flour, you can add 1 1/2 teaspoons baking powder and 1/4 teaspoon salt per cup of all-purpose flour.