Want a Foldable Phone? Hold Out for Real Glass


Foldable phones like Samsung’s Galaxy Fold and Huwaei’s Mate X are coming, whether you’re ready or not. In fact, they’re coming whether they’re ready or not. The software remains untested or nonexistent. The prices are either astronomical or unannounced. But those potential issues can be fixed on the fly. The real thing you should hold out for? Glass.

Yes, glass. The stuff that you tap when you use your smartphone, that you take for granted until you manage to shatter it on the sidewalk. Glass is strong, and durable, and hard to scratch and easy to see through to the bright and shiny OLED pixels below. Glass can even fold, probably further than you’d think. But it can’t flex far enough for smartphones that open up like books. At least, not yet.

“Glass today, the current choices out there, they’re not optimal” for folding smartphones, says John Bayne, who heads up glass giant Corning’s Gorilla Glass business. “In a glass solution, you’re really challenging the laws of physics, in that to get a very tight bend radius you want to go thinner and thinner, but you also have to be able to survive a drop event and resist damage.”

Instead, the early folding phone manufacturers are leaning on plastic polymers. Which makes sense in that the materials can not only bend as far as you’d need, they can do so repeatedly; Samsung claims its so-called Infinity Flex Display can withstand hundreds of thousands of openings and closings.

“The polymer is better at flexibility; it’s easier to bend at the same thickness,” says John Mauro, a professor of materials science and engineering at Penn State University who had previously spent 18 years at Corning.

But plastic is also, as you may by now have guessed, worse at all kinds of things. It’s much less hard than glass, which makes it easier to scratch and ding up. And unlike glass, plastic will crease over time, leaving you with a large unfolding display, sure, but one bisected with an unsightly wrinkle.

“With the polymer, the molecules can rearrange themselves more easily in response to stress, whereas the glass has a more rigid structure, so the response of the glass is going to be more elastic,” says Mauro. “The structure of the glass will be able to recover after the deformations.”

Don’t take two glass guys’ word for it. “The fact that you’re touching [that kind of display] with your nails is scratching it,” Motorola executive Dan Dery told Engadget in a recent interview, about a plastic film cover his company had prototyped. “It has a short life right away; it starts dying the day you unpack it.”

Or just look at how Samsung, Huawei, and others have staged the introduction of their foldable devices. Reporters haven’t been allowed much time to actually handle them, in part because the software’s not fully baked, but also because the display deviates from the glass cover the last decade has conditioned smartphone owners to expect. They’ve largely confirmed, though, that the difference is noticeable. It will only become more so over time.

Which means that foldable smartphones won’t be ready until glass is ready. Fortunately, that may be sooner than you’d think. Corning is working on ultra thin bendable glass that’s 0.1 millimeters thick, and can bend to a 5 millimeter radius. The trick, though, is achieving that kind of pinch without losing the toughness that makes glass great to begin with.

“The back of the problem we’re trying to break, the technical challenge, is can you keep those tight 3-5mm bend radii and also increase the damage resistance of the glass,” says Bayne. “That’s the trajectory we’re on.”


To get there, Corning is combining its experience with Willow glass, which can roll up like a ream of paper, and Gorilla Glass, which gets its strength from an ion exchange process. In fact, it’s that process that makes Willow Glass unsuitable for phones. It involves dipping glass into a molten salt solution, where potassium ions enter and push out smaller sodium ions, creating a “compressive stress layer.” To borrow an example from Corning think of what would happen if you replaced the billiards balls in a rack with tennis balls, which are slightly larger. The additional compression would make it much harder to roll the rack. In a sense, it’s stronger. But it also comes at a cost.

“In a display application, you’re putting transistors on the glass. Transistors hate salt: Sodium, potassium, anything from the salt family will eat away a transistor,” says Bayne. “For this family of glasses to work you have to have these components in the glass that are incompatible with transistors.”

Corning’s ultrathin bendable glass attempts to square that circle, but hasn’t quite yet. “We have glasses we’ve sampled to customers, and they’re functional, but they’re not quite meeting all the requirements,” says Bayne. “People either want better performance against a drop event or a tighter bend radius. We can give them one or the other; the key is to give them both.”

Bayne expects foldable glass to be ready by the time foldable smartphones go mainstream, say a couple of years. Mauro thinks Corning and competitors like Japan’s AGC may be even closer than that. But the important thing for you to know is that it’s not here now. Until it is, maybe spend that $1,980 on something a little more fully baked.

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