Mumbai [India], October 14: Apple has revealed a key engineering innovation behind the cooling system of its first foldable smartphone, the iPhone Duo. In an interview with PCMag, Apple engineers explained how a flexible graphite pipe routed through the device’s hinge helps transfer heat between its two halves, addressing one of the major thermal challenges associated with foldable smartphones.
The device is powered by Apple’s A20 Pro chip, which also features in the iPhone 18 Pro and iPhone 18 Pro Max. According to Apple’s engineering team, designing a single processor platform for both conventional smartphones and a foldable device required different approaches to managing heat, particularly because of the iPhone Duo’s thin profile and dual-display design.
Unlike a conventional smartphone, a foldable device has two sections connected by a hinge. When the phone is closed, the two halves sit together, creating a different internal arrangement for heat dissipation. Apple’s engineers developed a flexible graphite pipe that passes through the hinge to transfer heat between the two sides, increasing the surface area available for cooling.
Banafsheh Barabadi, Apple’s senior manager of thermal product design, described the hinge-based solution as one of the most technically challenging aspects of the device’s development. The flexible component must maintain its thermal connection and structural integrity through repeated opening and closing of the phone over its lifetime.
Apple has also redesigned the internal architecture of the A20 Pro platform to improve thermal efficiency. Instead of stacking the DRAM memory directly above the processor, the company moved the memory alongside the chip. This arrangement provides a more direct path for heat to reach the cooling system while allowing the components to communicate efficiently.
Another important component is the redesigned vapour chamber. Apple says the chamber used in the iPhone 18 Pro models has approximately three times the surface area of the one in the iPhone 17 Pro. The chamber helps distribute heat away from the processor and also serves as a structural element supporting internal components, including the battery and logic board.
The company has introduced a material it calls “metal over foam” between the processor and the vapour chamber. This creates a close thermal connection while accommodating the mechanical requirements of the internal assembly. Apple engineers said developing the material properties required months of work.
A new copper display plate and a high-conductivity graphite layer also contribute to heat management. These materials help spread heat across the display area rather than allowing it to concentrate in specific hotspots. Together, the components form a broader thermal-management system designed to support sustained workloads such as gaming, video recording and on-device artificial intelligence processing.
The A20 Pro version in the iPhone Duo also includes a second display engine to support the simultaneous operation of its inner and outer screens. Apple has additionally adapted the processor platform to support the FaceTime camera positioned behind the inner display.
The hinge-based graphite pipe stands out because it uses the foldable design itself as part of the cooling solution. Rather than treating the hinge only as a mechanical connection, Apple has integrated it into the thermal architecture to help move heat between the device’s two halves.
The engineering details offer a closer look at how Apple is addressing the performance and heat-management demands of foldable smartphones. The effectiveness of the system will ultimately depend on real-world performance across extended use, gaming, charging and other demanding tasks.
