Stuff Matters: Exploring the Marvelous Materials That Shape Our Man-Made World

by Mark Miodownik

How is it that this one material does so much for us, and yet we hardly talk about it? It is an intimate character in our lives—we put it in our mouths, use it to get rid of unwanted hair, drive around in it—it is our most faithful friend, and yet we hardly know what makes it tick. Why does a razor blade cut while a paper clip bends? Why are metals shiny? Why, for that matter, is glass transparent? Why does everyone seem to hate concrete but love diamond? And why is it that chocolate tastes so good? Why does any material look and behave the way it does?

What is it about paper that allows words to be expressed that might otherwise be kept secret? They are written in a private moment, and as such, paper lends itself to sensual love—the act of writing being one fundamentally of touch, of flow, of flourish, of sweet asides and little sketches, an individuality that is free from the mechanics of a keyboard. The ink becomes a kind of blood that demands honesty and expression, it pours on to the page, allowing thoughts to flow.

This layer, known as a laminate, is also the secret behind bulletproof glass, which is essentially the same technology but with several layers of plastic embedded at intervals within the glass. When a bullet hits this material, the outermost layer of glass shatters, absorbing some of the bullet’s energy and blunting its tip. The bullet must then push the glass shards through the layer of plastic beneath it, which flows like tough treacle, thus spreading the force over a wider area than the point of impact. No sooner has it got through this layer than the blunted bullet encounters another layer of glass, and the process starts all over again. The more layers of glass and plastic there are, the more energy the bulletproof glass can absorb. One layer of laminate will stop a 9-millimeter pistol bullet, three layers will stop a .44 Magnum pistol bullet, eight layers will stop a person with an AK-47 rifle from killing you.

Next time you are sitting in a café with little to do but watch the world go by, have a look at how people walk. It is kneeled—meaning that you push your knee out ahead of you, positioning it above the point where you wish to plant your next step, allowing the lower leg and foot to swing into place underneath it. Once planted, the foot has to adjust its angle to the terrain, twisting or tilting it, both of which also involve complex knee adjustments and realignment. Running is even more stressful on the knee as it must do all this while being buffeted by repeated impacts. Try walking without bending your knees and you’ll see how important this joint is to mobility.

At this microscale, materials scientists are starting to design structures that are able to control light. These so-called meta-materials can be formed with variable refraction indices, which means they can bend light any way they want to. This has yielded the first generation of invisibility shields, which when surrounding an object bend light around it so that from whichever direction you try to observe it, it appears to vanish.