In my review of Apple's iPhone Duo, I noted the engineering and build quality, how easy it is to unfold the phone, and also how solid and sure it feels when you close it. And I have opened and closed the flexible, dual-screen phone many, many times.When a small set of iPhone Duo owners complained that their large inner screens had unexpectedly and disturbingly cracked, Apple did something unusual: it acknowledged the complaints: "We are aware of an issue impacting the inner display on a small number of iPhone Duo units. If users experience issues with their iPhone Duo display, they should contact AppleCare for a replacement.”That's not Apple saying there's a fundamental flaw or that the issue is found on anything more than a small number of the already popular phones.I watched with some dismay as people started bandying about the 'crackgate' phrase. Apple has had its share of 'gates' over the years, including 'bendgate' with the iPhone 6 Plus, and Antenna Gate with the iPhone 4. On the latter, Steve Jobs memorably told customers they were holding the phone wrong (he later apologized for the issues).The notion of '[anything]gate' comes from the Watergate Scandal, a cover-up of a crime involving the then President of the United States, Richard Nixon. Now, whenever people think there's an issue and someone is trying to obfuscate it, they slap a 'gate' on it. I've written before that I hate this.Leaving aside the term, there is the fact that some people claim the iPhone Duo cracked when they opened it and only shortly after they brought it home. Since we can't rewind those tapes, we have to take them at their word. Still, I think it's fair to wonder if they opened it too roughly, like a strongman trying to tear a phonebook in half. We just don't know.Inside the iPhone Duo Display(Image credit: Apple)Here's what I do know, though: Apple spent considerable effort building a durable folding iPhone. Seriously, how could it not?Samsung has been doing this for a decade, and with each iteration of the Samsung Galaxy Z Fold line it has improved the display panel structure and supporting hinge technology. On the Galaxy Z Fold 8 Ultra it actually uses two titanium plates. One relatively rigid plate sits at the bottom of the stack, and is responsible for making the phone open stiffly flat. The other, for durability at the crease, is a super-thin sheet of titanium alloy.Apple does not talk about where it sourced its iPhone Duo display technology, though most have surmised that it started with Samsung. Even so, the display and hinge architecture of the iPhone Duo is distinct from that the Galaxy Z Fold 8 Ultra.It's worth digging into these details to understand the iPhone Duo's potential weak points, and because, in many of my conversations about why the Duo displays might have cracked and how it happened, people want to understand what part, exactly, is cracking. The build, as described by Apple on the Surprise and Shine launch day in September, provides some clues.It's been more than a month since Apple unveiled the iPhone Duo, but I recall Chief Hardware Officer Johny Srouji explaining in stark detail how Apple builds the iPhone Duo display and hinge (complete with images).According to Srouji, the goal for Apple was, unsurprisingly, "to provide the high quality for viewing content without what people dislike about foldable displays: The distracting crease, the plastic feel, susceptibility to scratches and dents."Apple started with what it knew and built something better(Image credit: Apple)Talking to me after the event, Srouji and Apple CEO John Ternus probably leaned a little too hard into criticisms of other foldable displays. Ternus claimed, "I think what you've seen out there are all these just kind of cheap-feeling plastic surfaces that don't feel good to the touch."Having used most of the major foldable phones out there, I don't think Ternus was being fair. After all, Apple has built its first foldable on the shoulders of giants like Samsung, who all but perfected the display design. Did Apple take it further? Absolutely.In the keynote, Srouji said Apple's engineers relied on "their learnings from iPad and Mac" to develop the biggest folding display innovation: the nano-texture display. This reflection-killing surface is what's primarily responsible for hiding virtually all visual remnants of the crease.(Image credit: Apple)I don't think the nano-texture covering (a polymer with a special anti-scratch coating, by the way) has anything to do with the possible cracks; instead, they probably relate to the multi-layered construction, and both the display and the hinges' ability to withstand thousands and thousands of folds (or, in the case of these cracked Duo screen customers, one bad unfold).Based on the images Srouji showed off, the iPhone Duo display is composed of 10 layers. Included in them is a back panel of titanium (yes, like on the Galaxy Z Fold 8 Ultra) for straightness and stiffness when unfolded. There are also two ultra-thin flexible glass layers above and below the OLED panel.Instead of these floating freely, Apple uses an elastic adhesive to keep the panels together while also letting them slide back and forth over each other so that, Srouji said, "the panel doesn't distort over time".Behind the panel is the hinge, which Apple says has one hundred components, some of which are attached to carbon fiber support plates.Watch this space(Image credit: Apple)My point is that Apple was about as open as a tech company could be about how and why it made the iPhone Duo display, and we have enough information to make at least one reasonable assumption: one or more of the thin glass panels cracked for a few iPhone Duo owners. After all, the OLED panel is about as flexible as a thin piece of plastic. The titanium wouldn't crack; even the nanostructured polymer is unlikely to crack. My guess is that either a manufacturing imperfection or misuse resulted in one or both of the glass panels cracking, and possibly damaging the OLED sandwiched between them.There are other hypotheses, like some loose component inside getting sandwiched and cracking the screen or even hinge misalignment. I'm sure Apple is examining every possibility.The iPhone Duo is the first iPhone with a significant moving part. It's the first with two displays. And the first where one is a flexible display that's expected to survive tens of thousands of folds. The complexity and quality assurance for building such a device is surely enormous. Apple is lucky to have had others like Samsung, Motorola, and Google go through a decade of perfecting the technology before it delivered the iPhone Duo. Still, that doesn't diminish its accomplishment. Nor does it lessen the risks of shipping a folding iPhone to people who don't always know when to stop unfolding. Maybe someone over-torqued it; maybe they just got a bad unit.In the end, such issues are not entirely unexpected, but they do not, for now at least, indicate a larger issue. I think Apple did its homework here, and I'm simply not buying 'crackgate.'