What’s the largest, fastest growing, organ in the human body? It’s the tough, elastic, flexible, and waterproof covering that helps protect other organs and body parts from such things as germs, heat, cold, and sunlight—skin, of course! This life science activity engages middle school students in an exploration of the structure, function, and variety of skin. They “construct” skin layer by layer using simple materials such as felt, foam padding, yarn, and vinyl in various skin tones. This activity provides an opportunity to discuss racial diversity and to show students that skin color is, quite literally, only skin deep.