The moment a crack forms in a piece of glass, it is prone to spread. That’s because although glass is very strong and resistant to deformation, it lacks the toughness that metals like aluminum and steel have.

Now, researchers from the California Institute of Technology and the University of California, Berkeley, report that they have devised a new type of metallic glass that is as strong as glass, but as tough as steel  the toughest of all metals.

“Typically with materials it’s very hard to get both toughness and strength; either you get one or the other,” said Marios Demetriou , a materials engineer at Caltech and the study’s lead author.

He and his colleagues report their findings in the journal Nature Materials.

There is, however, a catch to the seemingly transformational discovery.