Apple routed a flexible graphite pipe through the iPhone Duo’s hinge to move heat between the phone’s two halves. Foldables face a cooling problem that slab phones do not, because the iPhone Duo doubles in thickness once it is closed.
Banafsheh Barabadi, Apple’s senior manager of thermal product design, explained the approach in an interview with PCMag. She said the graphite pipe increases the surface area available to dissipate heat, and that Apple’s thermal and mechanical teams had to design it together.
This was one of the most technically challenging aspects of our design.
The pipe is flexible, so it has to survive many hinge cycles while keeping its thermal connection and structural integrity across the life of the phone.
The iPhone Duo Gets Its Own Thinner Vapor Chamber
The iPhone Duo uses a different vapor chamber from the iPhone 18 Pro and iPhone 18 Pro Max. It is thinner, and it floats in the middle of the phone instead of acting as the central structural plane, which is the role it plays in the iPhone 18 Pro. It still connects to the A20 Pro through a material Apple calls metal over foam.
The hinge is a major piece of that design. Apple’s iPhone Duo announcement says it is engineered from more than 100 components, and Apple’s hardware engineers have already said the hinge was the hardest problem to solve.
Moving the Memory Beside the A20 Pro Opened a Direct Path for Heat
Earlier iPhone chips used package-on-package construction, with the memory stacked on top of the processor. Dan Murray, Apple’s vice president of silicon engineering, told PCMag that stack limited how well heat could leave the chip.
The A20 Pro uses a wafer-level multichip module instead, which places the memory next to the processor. That lets the chip connect straight to the vapor chamber. The iPhone Duo version adds a second display engine to drive the inner and outer screens at once, and it supports the FaceTime camera behind the inner display.
Barabadi described four changes behind the cooling system in the iPhone 18 Pro, most of which apply to the iPhone Duo as well.
- Direct silicon access, since the memory no longer sits on top of the chip
- A metal over foam layer that couples the chip to the vapor chamber
- A vapor chamber with three times the surface area of the iPhone 17 Pro version and more de-ionized water inside
- A nanotube copper plate behind the display, paired with a high-conductivity graphite layer, to spread heat across the screen
In its iPhone 18 Pro announcement, Apple claims up to 40 percent better sustained performance than the iPhone 17 Pro, and it quotes up to 35 percent for the iPhone Duo. That fits with the larger vapor chamber a teardown of the iPhone 18 Pro found earlier.
The iPhone Duo starts at $1,999 in the US. Pre-orders open Friday, October 16, and the phone is available Friday, October 23.
