Rubber and steel are at different ends of the spectrum when it comes to hardness, and wherever an object falls on that scale is typically where it will stay. But researchers at the University of Michigan have now developed a metamaterial that can change the stiffness of its surface, from hard to soft and back, in response to a small amount of stress. 

As artificial materials that can be finely tuned for a specific purpose, metamaterials can do some pretty incredible things that you won't find in nature. Interestingly, what they're made of doesn't seem to matter: instead, their attributes stem from their structure, and by manipulating that, engineers can develop metamaterials that could replace optic lenses, make objects effectively invisible, or create vehicle parts that are both very strong and very light.

The University of Michigan team says its new metamaterial specializes in switching its surface between hard and soft states. Applying a small amount of strain allows that stiffness to be changed by several orders of magnitude, without damaging or weakening the material itself.