When it comes to donuts, there are a few things that make them fluffy. One is the type of flour that is used. A lighter flour will make for a lighter donut, while a heavier flour will make for a denser donut. Another factor is how much leavening is used. Too much leavening will make the donut tough, while not enough will make it dense. The perfect amount of leavening will make for a fluffy donut. Finally, the amount of fat in the recipe will also affect the donut's fluffiness. More fat = more fluffy. So, if you're looking for a fluffy donut, make sure to use a light flour, the perfect amount of leavening, and a good amount of fat.