What causes Bread to be fluffy? What kind is bread of the fluffiest?

Carbon Dioxide makes bubbles in the dough that make the bread fluffy. I think white break is the fluffiest.

Well it's simple, bread flour has an increased amount of protein or more gluten which results in a lighter, fluffier dough which produces a less dense finished product. All-purpose flour can be used for bread but bread flour is always better if your goal is a “fluffier” bread.