one-way glass
(Ihar Faniayeu/Aalto University)

Scientists Have Designed the World’s First True ‘One-Way Glass’ Using the Magic of Metamaterials

Like something out of a science fiction crime drama, a team of metamaterial scientists from Aalto University says they have designed a new material that will enable the world’s first true one-way glass.

Unlike current technologies that limit the flow of light through glass, this metamaterial would be the first to allow virtually all of the light to pass through the glass in one direction while reflecting virtually all of the light coming in the other direction.

“Glass that’s currently sold as ‘one-way’ is just semi-transparent, letting light through in both directions,” explains a press release announcing the metamaterial breakthrough. “When the brightness is different between the two sides (for example, inside and outside a window), it acts like one-way glass. But an NME-based one-way glass wouldn’t need a difference in brightness because light could only go through it in one direction.”

Building ‘Police Drama’ One-Way Glass in the Real World

Of course, one-way glass is a hallmark of police dramas, where it is regularly employed to protect the identities of witnesses picking through a lineup of would-be suspects. In real life, most police line-ups involve cameras in separate rooms, ensuring that the suspects don’t know the identity of their accuser.

Still, there are a number of much more practical uses for a glass that is transparent on one side and perfectly reflective on the other. Some involve improved harvesting of energy, but many simply involve the same desire for privacy that drives fictional one-way glass in police stations.

“Just imagine having a window with that glass in your house, office, or car,” said Shadi Safaei Jazi, a doctoral researcher at Aalto University and one of the scientists behind the exciting research. “Regardless of the brightness outside, people wouldn’t be able to see anything inside, while you would enjoy a perfect view from your window.”

Traditional materials used to make glass have been unable to achieve such a feat, but the Aalto team believed the key to creating true one-way glass could lie in the modern field of metamaterials. More specifically, they hoped to take advantage of something called the nonreciprocal magnetoelectric effect (NME).

According to the release, “The NME effect implies a link between specific properties of the material (its magnetization and polarization) and the different field components of light or other electromagnetic waves.”

In more practical terms, the ability to artificially manipulate this effect (which is negligible in natural materials but theoretically possible in metamaterials) would open up all kinds of commercial and industrial applications where the flow of electromagnetic energy, including light, is desired in one direction but not in the other. This includes true one-way glass. Unfortunately, the Aalto researchers say previous efforts to capitalize on this phenomenon have been met with failure.

“So far, the NME effect has not led to realistic industrial applications,” said Jazi. “Most of the proposed approaches would only work for microwaves and not visible light, and they also couldn’t be fabricated with available technology.”

Metamaterial Realizes NME Breakthrough

In their published research, which appears in the journal Nature Communications, the Aalto University researchers say they have succeeded in breaking through both of those barriers. The result is the first-ever design of an optical NME metamaterial “that can be created with existing technology, using conventional materials and nanofabrication techniques.”

Along with the promised benefits to privacy, the researchers say one-way glass created with their metamaterial design could be placed on top of existing solar panels and capture much of the reflected heat energy that is lost with current designs. It could also replace safety glass, car windows, or even one-way sunglasses that don’t result in any dimming.

Oh yeah. It could also probably help your favorite cable crime fighters finally ID the slippery suspect once and for all.

Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at, or email him directly at