On October 21, 2026, HTX Studio published a review in which it analyzed Apple's foldable smartphone, the iPhone Duo, with CT (computed tomography) and recreated the internal structure of its hinge as a 3D model. According to Apple, the hinge is made up of more than 100 parts. It links the movement of the left and right halves of the body and can hold the screen at intermediate angles. The scan let the reviewers examine the inside of the device, which went on sale in Japan on October 23, without taking it apart. The review also tested the screen's durability. Even with design measures meant to make the crease less noticeable, the screen's shape changed after testing meant to simulate use.
Gears synchronize the two halves; a spring and cam hold the angle
HTX Studio's analysis divides the hinge into six functional areas. Paired mechanisms sit at the top and bottom, and the center leaves a channel for the flexible cable that connects the circuitry on the left and right. Because the reviewers could not disassemble their review unit, they say they built the 3D model by combining CT images with Apple's official materials. This differs from a teardown, in which parts are physically removed and examined, but it makes it possible to see how mechanisms that are hidden from outside are arranged and how they work.
The two halves of the body are connected to a central axis, and each one rotates. Gears link the two sides, so when one side moves, the other rotates by the same angle, keeping both halves in step even when the phone is opened with one hand. Holding the open screen at an intermediate angle is the job of a spring and a "cam." A cam is shaped so that the amount it pushes against a contacting part changes with its rotational position. When the screen is folded, the spring is compressed, and its resistance and friction resist rotation. That resistance counteracts the rotation that the weight of the body would otherwise cause, allowing the screen to be held at any angle.
In HTX Studio's hands-on testing, the screen held its angle across a range of 15 to 165 degrees. However, this is a result confirmed on the review unit, not a range Apple guarantees for every device or under all conditions. When the screen is closed, magnets built into the body pull the two halves together. Different parts share the roles: gears synchronize the rotation of the two sides, the spring and cam hold the angle, and magnets keep the phone closed.
3.85mm is not the depth of the crease
The roughly 3.85mm dimension measured from the CT images refers to the maximum width of the space in which the display bends into a teardrop shape internally when the screen is closed. It is neither the depth of the crease that appears on the screen surface nor the radius of the bend. The design provides room for the display to form a gentle curve inside instead of being folded sharply.
According to Apple's official explanation, the hinge also serves as a structure that supports the center of the display when it is open. The screen itself is a laminated structure that combines multiple materials, with high-strength glass layers above and below the display panel. The layers are bonded with a proprietary adhesive, and when the screen is folded they slide against one another like the pages of a book to accommodate the deformation. The surface uses a polymer cover layer and a scratch-resistant coating, and a titanium plate is placed beneath.
To understand this construction, it helps to distinguish between the mechanism that controls the hinge's movement and the measures that reduce stress on the display and improve how the crease looks. Putting HTX Studio's analysis and Apple's official explanation together, the roles break down as follows.
| Role | Main parts / measures | What it improves |
|---|---|---|
| Synchronizing left and right movement | A mechanism combining gears and rotating shafts | Rotation of the left and right halves |
| Holding the angle | Spring and cam | Rotation caused by the body's own weight |
| Bending and supporting the display | Teardrop-shaped bending space, sliding laminated structure, center support mechanism | Stress when folded and support when unfolded |
| Reducing reflections | Nano-texture finish on the surface | How reflections look near the crease |
This table classifies the role of each part. It is not a comparison of product lifespan or of superiority over other companies' products. The structure of the hinge and display reduces stress during folding, while the surface treatment improves how the crease looks. They are different mechanisms, but they share the goal of making the crease less noticeable.
According to HTX Studio, on a glossy screen, reflections distort along the curved surface of the crease, making irregularities easier to see. The Nano-texture finish scatters light, which can reduce this distortion of reflections. The reviewers also point out, however, that in environments with ambient light, black areas can look grayish. There is a trade-off between suppressing reflections and display contrast.
After 3,000 folds, the crease's height difference grew from 48μm to 167μm
In HTX Studio's test, the height difference between the peak and valley of the iPhone Duo's crease changed from 48μm before the test to 167μm. In the test, the screen shapes of a new iPhone Duo and a new foldable smartphone from another company were measured, then each was opened and closed 3,000 times by a machine, kept closed for a set period, and measured again. On the iPhone Duo, the slope of the central crease also changed, increasing from less than 0.1 degrees before the test to 1.24 degrees afterward.
| iPhone Duo measurement | Before testing | After folding and storage while closed |
|---|---|---|
| Height difference between crease peak and valley | 48μm | 167μm |
| Slope of the central crease | Under 0.1 degrees | 1.24 degrees |
The figures are based on the review HTX Studio published on October 21. However, because the post-test measurements reflect not only 3,000 folds but also storage while closed, it is impossible to separate how much each condition contributed to the change in shape. Details such as the measuring equipment, the number of units tested, temperature and humidity, and how long the phone was kept closed are also not fully clear from the explanations we could find. This result therefore cannot be treated as the average change across all products or as an indicator of lifespan under long-term use.
Still, the test highlights an important point in evaluating foldable displays: a crease that is inconspicuous on a new device is not necessarily one whose shape will hold up over a long period. The Nano-texture finish may make changes in the crease less noticeable by reducing reflection distortion, but the surface treatment itself does not eliminate the irregularities. To judge real-world usability, it matters to compare the screen not only as it looks when new but also after repeated folding, under the same lighting conditions.
Scratch resistance of the surface is a separate question from long-term durability
HTX Studio also ran a scratch test on the inner display using pencils from 6B to 8H. With a fixture applying a constant downward load equivalent to 100g, 6H left a faint scratch visible under strong light, while 8H produced a distinct scratch that could be felt by touch. The H and B here denote pencil hardness grades, which differ from the Mohs scale used for the hardness of minerals. The result of rubbing a pencil under a constant load cannot be applied directly to resistance to scratches from contact with keys, sand, and the like. The same goes for the Apple Pencil, which Apple plans to support within 2026: writing feel and surface wear from long-term use need to be evaluated separately.
The materials of the body and hinge also need to be understood distinctly. Apple says it uses grade 5 titanium for the body and provides a 3D-printed cover on the outside of the hinge. That does not mean the internal gears and springs are all made of titanium. Moreover, how well the outer cover protects the internal mechanism and whether the moving parts can maintain adequate holding force after repeated movement are separate evaluation items.
The IP68 rating for dust and water resistance also comes with constraints on test conditions. According to Apple, the iPhone Duo meets the rating under controlled laboratory conditions, at a maximum depth of 6 meters for up to 30 minutes. At the same time, splash, water and dust resistance are not permanent and may decrease with normal use. Even if the device meets IP68 when new, that does not guarantee its sealing after long-term use.
Can apps make use of a hinge that stops partway?
Apple's design guidelines envision uses such as holding the iPhone Duo partly open like a book, placing it on a desk, and standing it on its side. A hinge that can hold a stable intermediate angle is not just a mechanism for folding the screen; it also gives users more freedom in how they hold and place the device. But even if the hardware supports these uses, the benefits can't be fully realized unless apps behave properly.
Apple asks developers to avoid layouts that assume a fixed width and to design content that adapts flexibly to the available display area. It is also important that features and operating state carry over when switching between the inner and outer displays. When the screen is folded partway, care is needed not to place controls such as buttons near the crease. It's not only the screen size that changes: apps are tested on whether they can switch to a layout that is easy to operate depending on the device's posture.
The iPhone Duo goes on sale in Japan on October 23, and evaluations with real devices will begin. Going forward, the points to watch are whether it stops stably at the desired angle after repeated folding, how the look of the crease changes with use, and whether everyday apps can handle the various ways of holding it. Only when the hinge mechanism, display durability and software support come together can the ability to use the phone partly open become a practical advantage that reduces the effort of supporting the device in hand and of switching screens.