Auxetics, new materials for lightweight body and vehicle armor that strengthen when a bullet strikes

What do a flea and an eagle have in common? They can store energy in their feet without having to continuously contract their muscles to then jump high or hold on to prey. Now scientists Now scientists at Queen Mary University of London and University of Cambridge have created materials that can store energy this way, be squeezed repeatedly without damage, and even change shape if necessary. These kinds of materials are called auxetics and behave quite differently from regular materials. Instead of bulging out when squeezed, they collapse in all directions, storing the energy inside.