Many years ago, my parents and brother were driving home late at night, full speed on a highway, when a large rock thrown off an overpass struck their car’s windshield. There was a time when an impact like that would have shattered the windshield glass, likely leading to a tragic accident and – for me – a painful childhood. But, thanks to the modern miracle of laminated safety glass, the windshield did not shatter; it only cracked. The rock rolled away, my dad maintained control of the car, and the three of them got home safe and sound.

One of the lessons of that night is that in many applications, the mechanical strength of glass is every bit as important as its transparency. However, there’s a reason we don’t often see literal glass ceilings. The problem is that glass breaks before it bends – even the tiniest fracture spreads rapidly in all directions until the entire pane shatters. In engineering terms, glass is strong (it can withstand a lot of stress before cracking) but not tough (it has little damage tolerance after the onset of cracking). This is in contrast to sheets of metal or plastic that can deform to accommodate small defects, making them generally tougher materials.

To a group of researchers at Lawrence Berkeley National Laboratory and Caltech, this begged the question: is it possible to engineer tougher glass by making it behave more like metal? The answer, it turns out, is yes.

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