If your cat swats your iPhone 4 across the room, there's a good chance the iPhone will smash against a wall or the floor and, sadly, one of the glass screens will crack\u2014at least twice the chance as with the iPhone 3GS, because the iPhone 4 is double-sided.How delicate is the iPhone 4 glass? SquareTrade, an iPhone warranty provider, reported that iPhone 4 screens break a whopping 82 percent more than iPhone 3GS screens.[ Insurer reveals five strange ways iPhones die, reports CIO.com. | Check out three cons beneath sleek iPhone 4 design. ]iPhone 4 models aren't known for their overall durability: 4.7 percent of iPhone 4 owners reported damage in the first four months, compared with 2.8 percent of iPhone 3GS owners, according to SquareTrade. This has at least one tech manager worried about bringing iPhones into the enterprise."Drop it, and we have to buy another one at full price," Shane Allen, former information systems manager at Special Devices, a manufacturer of air-bag initiators for the automotive industry, told CIO.com earlier this year. "But you can drop kick a BlackBerry or candy bar phone or flip phone."Two-thirds of all iPhone accident claims fall into three categories\u2014liquid damage, cracked screens and theft\u2014says Aaron Cooper, marketing director at Worth Ave. Group, a consumer electronics insurer. "We're seeing more accidents, probably because people are more attached to their iPhones and iPads than ever before," Cooper says."The iPhone 4 breaks more," says Kyle Wiens, CEO of iFixit, a website that provides free repair manuals and advice forums mostly aimed at Apple products. So what's behind the iPhone 4's higher risk of a cracked screen? Sure, the iPhone 4 has glass on both front and back, thus having twice as much glass as the single-sided iPhone 3GS\u2014but there's more to it.Perhaps the biggest reason for the iPhone 4 screen's susceptibility to breakage: The iPhone 4 glass extends to the edges of the phone. An impact on the edge, say, a fall on concrete from only a couple of feet in the air, will shatter the glass, says Wiens, because the glass directly takes the impact.On the iPhone 3GS, though, a relatively large metal ring surrounds the edge. The metal ring is a lot more forgiving than glass and thus can better handle such an impact, Wiens says.Apple claims iPhone 4 screens are 30 times harder than plastic and comparable to sapphire crystal, yet that's part of the problem, some Apple iPhone experts say. Hardness makes the screen more scratch resistant, but not as elastic. Given plastic's elasticity, there's less chance of the plastic shattering. "Yes, the [iPhone 4 screens] are 30 times harder and so they're going to break more," Wiens says.On the upside, the iPhone 4 front glass is glued securely to the liquid crystal display. This structural support makes the glass more tolerant to impact than the non-glued glass of the iPhone 3G and 3GS, Wiens says. But the iPhone 4 back glass is not glued. "We're seeing the back glass break more often than the front screen," he says.Another possible factor for the higher rate of iPhone 4 broken glass: Think screen protectors, says Worth Ave. Group's Cooper. In the past, almost every iPhone owner put a screen protector (a thin film with a sticky side) on the glass. Then Apple said improvements to the glass, starting with the iPhone 3GS, made screens highly scratch resistant and thus screen protectors were no longer needed.Earlier this year, Apple banned iPhone screen protectors from Apple Stores (although screen protectors are still available from third parties). So it's unlikely iPhone 4 owners have purchased and put on a screen protector, let alone two.Screen protectors, though, protect iPhone screens from much more than scratches\u2014they can prevent glass from shattering, according to Worth Ave. Group. At this year's MacWorld Expo, Worth Ave. Group put on a demonstration asking attendees to smash screens of various models of iPhones with a hammer. Screens without a screen protector broke easily, while those with a screen protector did not break. Cooper is considering handing out free screen protectors to Worth Ave. Group's iPhone customers. Screen protectors might be a good idea for all iPhone 4 owners. Tom Kaneshige covers Apple and Networking for CIO.com. Follow Tom on Twitter @kaneshige. Follow everything from CIO.com on Twitter @CIOonline. Email Tom at firstname.lastname@example.org.