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Corning says Gorilla Glass trumps sapphire screens, but the truth is more nuanced

Corning claims Gorilla Glass is a better, more durable display material than sapphire--but is it true?

Corning has begun a pre-emptive strike against a competitor to Gorilla Glass, its product widely used in the displays of many smartphones.

The company has posted an article to the Web previewing the next generation of its product, as well as a stress-test video.

In its article, Corning maintained that Gorilla Glass has a number of benefits over sapphire as the cover glass for mobile devices, such as smartphones. It asserts that Gorilla Glass is lighter than sapphire; consumes less energy and costs less to produce; is brighter; is thinner so it can be curved and more responsive to touch; and is stronger.

In a stress test, Corning shows a smartphone-sized, 1mm thick sheet of sapphire breaking after 161 pounds of pressure is applied to it, while the Gorilla Glass remains unbroken after 436 pound of pressure is applied to it.

"Discussion seems to center around sapphire as an obvious solution for a cover material," Corning Senior Vice President Jeffrey W. Evenson explained in the company's article.

"What would people say if someone invented a cover that was about half the weight, used 99 percent less energy to make, provided brighter displays, and cost less than a tenth of sapphire?" he asked. "I think they'd say that sapphire was in real trouble."

"It so happens that we at Corning already invented that cover--and it's called Gorilla Glass," he said.

Immunity to scratching

While Corning's test suggests that Gorilla Glass may be more resistant to sheer pressure, the claims don't address a major draw for sapphire screens. One of the applications for sapphire has been in high-end watches because it's immune to scratching. Only diamond or other sapphire can scratch sapphire.

Corning does have something to say about those watches, however.

"Those covers are much smaller than a mobile phone and are two to three times thicker than Gorilla Glass," James R. Steiner, senior vice president and general manager of Corning's Specialty Materials segment, said in the Corning article.

Sapphire's immunity to scratching is also the reason Apple uses it to protect the iPhone 5's camera lens, and may use it to protect the rumored fingerprint reader in the next version of its smartphone.

While Gorilla Glass has a broad appeal--it's in 1.5 billion consumer electronic devices, according to Corning--sapphire has largely been used in specialty applications: a component in LEDs, sensor windows in aircraft, and military uses.

Sapphire strikes back

The barrier to sapphire being used as a smartphone cover isn't strength, but cost, noted Jeff Nestel-Patt, director of marketing for GT Advanced Technology, a maker of sapphire.

"What's kept sapphire from becoming a more mainstream product that you'd find in consumer devices has been related to the cost," he told PCWorld. "But it's coming down in its price and it's now reaching levels where it's viable to start looking at broader, higher volume markets."

A typical smartphone display made from Gorilla Glass costs less than $3, while a comparable sapphire screen would cost $30, although that might come down to $20 in a couple of years because of competition and improved technology.

Because of those costs, sapphire will probably start entering the consumer market at its edges in products that need sapphire's durability and scratch immunity but are not sold in high volumes.

"Things like ruggedized devices," Nestel-Patt said, "products made to operate in harsh envrionments that are produced in lower volumes and are not price sensitive."

He said that his company has enlisted independent testers to take the measure of sapphire. "The results that we're seeing are very positive," he said. "We believe that in terms of durability and scratch resistance it outperforms Gorilla Glass."

Since no head-to-head independent durability test results have been released to date, claims about the merits of the two materials is largely a case of he said, she said.

Staying strong

As smartphone screen sizes get bigger, durability is a big issue, observed David Anderson, director of product marketing for ProtectYourBubble.com, whose insurance lines includes smartphone breakage insurance.

But durability may be a function of design as well as materials.

"We're seeing twice as many damage claims from Samsung S devices than iPhones," he told PCWorld. "We think that has a lot to do with design."

"If you drop an iPhone, that stainless steel rim around it protects the phone if it hits the ground on its side," he explained. "The Galaxy S3 is much more fragile around the edges and is a slick device that can slip out of your hand. It doesn't take much for that glass edge to hit the concrete and break."


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