Bill Hammack is a professor in the Department of Chemical Engineering at the University of Illinois. Online, he’s known as the Engineer Guy to his nearly 500,000 YouTube subscribers.

In this video, Bill reveals the stunning engineering underlying the design of the disposable diaper. He describes the five layers of a diaper, including the superabsorbent polymer in the diaper’s core. He illustrates the action of this polymer with a demonstration using a single bead of polymer: it soaks up enough water to grow from a diameter of 4 mm to nearly a half inch.