Early iPhone Duo reviews disagree on how hot Apple's first foldable gets, with some reviewers calling it merely warm and others saying it struggled under sustained load, according to a MacRumors roundup of the coverage published ahead of Friday's launch.
Warm in some hands, a problem in others
Joanna Stern said the back of her review unit grew warm during FaceTime calls and photography, and that she had to end one call because the phone got too hot. She said Apple told her the warmth reflects a thermal design that moves heat away from the chip to preserve performance. The Verge reported the phone heated up during long camera sessions, particularly with both displays active, and that noticeable lag followed. It also saw heat with third-party video and Google apps.
PetaPixel said its unit warmed during gaming, photo editing and other processor-heavy work, with the heat concentrated on the right side when unfolded.
Benchmarks tell a mixed story
In a 30-minute gaming test, HTX Studio measured 46.5°C on the iPhone Duo, against 43.8°C for the iPhone 18 Pro and 43.2°C for the iPhone 18 Pro Max. The channel also reported a frame rate about 20 percent lower than the Pro models and a drop in brightness from 300 nits to 185 nits. Mrwhosetheboss ran a 20-minute stress test against the iPhone 18 Pro Max and found the Duo trapped heat when closed and performed below the Pro Max, though he said the gap was not dramatic in everyday use.
Tom's Guide said the Duo spread heat evenly across its body but ran a few degrees warmer than Samsung's Galaxy Z Fold8. Its 3DMark stress stability score was 75.9 percent, versus 79 percent for the iPhone 18 Pro Max and 72 percent for the Z Fold8.
Others saw no issue
9to5Mac found the Duo runs slightly hotter than the iPhone 18 Pro without any effect on performance, and Gizmodo said heat was not a problem, with the vapor chamber keeping the phone from lagging or slowing when apps used every CPU and GPU core.
What the hardware does
MacRumors notes the Duo uses the same custom vapor chamber approach and A20 Pro chip as the iPhone 18 Pro, though its vapor chamber is thinner. A flexible graphite pipe in the hinge carries heat between the two halves, adding surface area for dissipation.
Because the phone only goes on sale on Friday, how it behaves over weeks of ordinary use is still unknown. These are early impressions from review units, and results vary by workload, app and conditions.
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