iPhone Duo uses a flexible graphite pipe in its hinge for cooling

Apple detailed the iPhone Duo's thermal design: a flexible graphite pipe runs through the hinge to move heat between the two halves. The Duo's A20 Pro also adds a second display engine and a FaceTime camera behind the inner display.

• A flexible graphite pipe in the hinge moves heat between the iPhone Duo's halves
• The Duo's A20 Pro adds a second display engine for both screens
• The FaceTime camera sits behind the inner display
• A 'metal over foam' material couples the SoC to the vapor chamber