The hinge of Apple's foldable smartphone, the iPhone Duo, contains flexible graphite tubes that carry heat to the left and right halves of the body. Apple engineers revealed the cooling design in an interview with PCMag, 9to5Mac reported on October 12. Apple had already said at its September launch that the phone includes a dedicated vapor chamber, but this latest explanation shows how the company gets heat out through a hinge that has to bend. The design addresses a problem specific to foldable phones, one that simply fitting a cooling component cannot solve. Still, how this cooling structure works and Apple's "up to 35%" sustained performance gain need to be considered separately.
Moving heat through the hinge to both sides of the body
The PCMag interview featured Dan Murray, Apple's vice president of silicon design, and Banafsheh Barabadi, senior manager of thermal design. According to them, graphite tubes run through the hinge and move heat between the left and right halves of the body, expanding the area available for dissipating heat.
Because the iPhone Duo changes shape as it opens and closes, any component that conducts heat must be flexible. It has to do more than bend: it must keep conducting heat after repeated flexing. Barabadi described this part of the design as follows.
"It was one of the most technically challenging parts of the design."
Both the thermal design and mechanical design teams worked on the tubes, reportedly because they had to maintain thermal conductivity through repeated opening and closing without problems in the shape of the material or its connection points. In other words, the iPhone Duo's hinge is not only a mechanism for folding the display but also a path for transferring heat to the other side of the device.
That said, it would be wrong to picture the "tubes" as hose-like structures with liquid circulating inside. What has been explained so far is a heat conduction mechanism using flexible graphite components. Whether any fluid is involved and the specific cross-sectional structure have not been disclosed. The vapor chamber itself also does not pass through the hinge. The basic principle of how heat moves was explained, but detailed information about the materials' structure has not been made public.
Moving heat efficiently from the chip to the whole body
Component placement around the A20 Pro has also been rethought to release heat more efficiently. According to the explanation given to PCMag, the DRAM that was previously stacked on top of the processor is now placed beside it. This makes it easier to transfer heat directly from the processor to the cooling components.
Between the chip and the vapor chamber, a special material made of foam wrapped in metal is used. Barabadi said this material not only conducts heat directly but also accommodates mechanical deformation. Efficient heat transfer requires components to be in close contact, but the structure must also withstand the deformation that occurs during use.
In its official September announcement, Apple also explained that new chip packaging technology connects the A20 Pro directly to a dedicated vapor chamber for efficient heat dissipation.
A vapor chamber is a cooling component in which a working fluid inside repeatedly evaporates and condenses, spreading heat over a wide area. The graphite tubes in the hinge, newly revealed, serve a different role.
Combining Apple's official announcement with this interview, the roles of each part are as follows.
| Location | Design approach | Main role |
|---|---|---|
| Around the chip | DRAM placed beside the chip; A20 Pro connected directly to the cooling component | Efficiently draws heat out of the processor |
| Between chip and cooling component | Foam material wrapped in metal | Conducts heat while accommodating mechanical deformation |
| Hinge connecting both halves | Flexible graphite tubes | Spreads heat to both sides of the body |
This table summarizes the role of each part and does not compare their heat dissipation performance. The structure around the chip and the vapor chamber draw heat out and spread it efficiently, while the tubes in the hinge carry heat to the opposite half of the body.
The iPhone Duo also has scenarios in which the inner and outer displays are used at the same time. According to Apple, features include showing a preview on the outer screen while shooting, and letting the person on the other side of the device join a FaceTime call.
This means the cooling design must account not only for gaming on the large screen but also for the use of multiple displays at once. Whether the phone can maintain processing performance across varied usage conditions is what matters.
The up-to-35% sustained performance gain is not an effect of the hinge alone
When it announced the iPhone Duo on September 9, Apple said the combination of the A20 Pro and an advanced thermal management system improves sustained performance by up to 35% compared with the iPhone 17 Pro.
The key point is that this figure of up to 35% reflects the performance gain from the A20 Pro and the thermal management system as a whole, not the effect of the graphite tubes in the hinge alone.
Apple's official description of "pro performance from the A20 Pro and advanced thermal management" can be summarized as follows.
| Item | What Apple has announced |
|---|---|
| Comparison | iPhone Duo vs. iPhone 17 Pro |
| Elements contributing to the gain | A20 Pro and advanced thermal management system |
| What the up-to-35% figure measures | Improvement in sustained performance |
| Conditions not disclosed | Duration of load, whether the device was open or closed, ambient temperature, effect of the hinge tubes alone |
Even comparing the September announcement with the October interview, it is impossible to determine how many percentage points of sustained performance the tubes in the hinge contribute.
For example, measuring performance with and without the graphite tubes while holding all other conditions constant would let their effect be isolated. But the figure Apple released is a comparison with the iPhone 17 Pro, which has a different chip and a different body structure. It does not measure the effect of the hinge tubes alone.
Similarly, it would be a mistake to interpret the up-to-35% figure as a reduction in body temperature, or to take it to mean the iPhone Duo is 35% faster than the iPhone 18 Pro. The comparison is with the previous-generation iPhone 17 Pro, and what is shown is sustained performance, not temperature.
This does not mean the tubes in the hinge have no effect. It means the published information alone does not allow their effect to be evaluated individually.
A cooling design making sense on paper is a separate question from how much performance the phone can sustain in actual gaming or video recording. Apple's explanation makes the design intent clear, but judging how much it contributes to real-world use requires testing on actual devices.
Balancing opening-and-closing durability with cooling performance
According to Apple, the iPhone Duo's hinge is made up of more than 100 parts, controlling the opening and closing motion while supporting the center of the display.
Because a heat-conducting component is built into this moving part, what matters is not only smooth operation and mechanical durability but also whether it can keep conducting heat stably over long-term use. This is likely why Barabadi emphasized the joint development by the thermal and mechanical design teams.
However, the explanation does not make it possible to determine a specific number of open-close cycles or cooling performance after long-term use. The design goal of maintaining the connection through repeated bending must be distinguished from test results showing how many open-close cycles the device passed and under what conditions.
To evaluate cooling on a real device, one approach would be to apply the same load with the phone open and closed, then compare processing performance and surface temperature after a set period.
For games, for example, what matters is not just the peak frame rate right after launch but how much performance is maintained over long play sessions. Shooting and video calls that use the inner and outer displays at the same time would also need to be compared under unified conditions.
If measurements could also be taken under the same conditions on devices that have been used for a long time, it would be possible to verify whether repeated opening and closing affects heat conduction performance.
The iPhone Duo opens for preorders at 9 p.m. Japan time on October 16 and is scheduled to go on sale on October 23.
The hinge cooling structure revealed this time is an interesting solution to the limited heat dissipation area of foldable smartphones. If a design that uses both halves of the body for heat dissipation works well on real devices, the phone may be able to maintain stable performance even in gaming that takes advantage of the large screen and in long work sessions.
Judging its true value will require hands-on tests with unified opening states and load durations. Post-launch evaluations will show how much of an advantage Apple's unique cooling design brings to the performance of a foldable smartphone.