Katia Bertoldi of Harvard held a holey plastic metamaterial that looked like a pink Connect Four board, with a regularly repeating arrangement of holes. When squeezing the material, some holes became horizontal ovals, as you would expect in an ordinary material. But other holes, when squeezed, became vertical ovals, because of the way the metamaterial was designed. As Bertoldi squeezed the material further, some of the horizontal ovals transformed into vertical ones and vice versa. This allows metamaterials to have very different mechanical properties than ordinary materials.
Bastiaan Florijn of Leiden University in the Netherlands showed what he said was the first “programmable” metamaterial. It was another holey plastic material, this time with clamps that control the forces. You could adjust the way the metamaterial compresses when you squeeze it, based on its design and the arrangement of the clamps. He said one of the future applications of this design could be car bumpers with variable stiffness. When backing up from your parking space, the bumper can be soft as a pillow in case it comes in contact with children, but on the highway it can be very rigid to protect occupants in a crash.