This experiment is about bread. If you have used my website for long, you know that I like experiments with food, especially when it is tasty food. We regularly bake bread, and there are few smells that are better than the smell of freshly baked bread.
Look carefully at a slice of bread. What do you see? Lots of holes, right. Depending on the type of bread, the holes may be small or large, but it will have lots of open space. To get an idea of just how much empty space there is, squeeze the slice of bread into a ball. Get it as small as you can, which should be quite a bit smaller than it was when you started. How did all those holes get in the bread?