Numerous iPhone Duo reviews have covered the device’s thermal properties, and reviewers’ opinions varied. Some found it was simply hot, while others thought it was too hot at times.
Joanna Stern said the back of the device got warm when using FaceTime and taking photos. Had to end a FaceTime call during testing because it was too hot. “Yes, I will burn my hand,” he said. “This thing is getting real hot.”
Apple told her the heat was a sign of the iPhone Duo’s thermal design that moves heat away from the chip to keep performance high. “But to me, it feels like the phone is really hot,” he said.
The iPhone Duo has the same custom vapor chamber setup and A20 Pro chip as the iPhone 18 Pro, but the vapor chamber is thinner. Apple added a flexible graphite tube in the hinge to transfer heat between the two halves, providing more surface area for heat dissipation.
The limit said the iPhone Duo gets warm when using the camera for an extended period, especially if both displays are turned on for features like Duo Preview. “When this happens, you can feel the phone getting much warmer,” the review reads. “The phone gets hot enough to start slowing down noticeably after a while.” The site also claims that it gets hot when running third-party apps, especially video apps and Google apps.
PetaPixel‘s review unit overheated while gaming, photo editing, or anything that stressed the processor, with the heat felt on the right side of the open device.
Mrwhosetheboss ran a 20-minute stress test with the iPhone Duo and iPhone 18 Pro Max. He found that the iPhone Duo trapped heat inside when closed, and the performance of the iPhone Duo was lower than the iPhone 18 Pro Max. When open, the iPhone Duo has a large display high resolution which also affects performance. Mrwhosetheboss focused more on performance than heat, and said that the difference between the iPhone Duo and the iPhone 18 Pro Max is not “hugely” noticeable in everyday use.
HTX Studio conducted a 30-minute gaming test with the iPhone Duo and iPhone 18 Pro models. The iPhone Duo was at 46.5°C, while the iPhone 18 Pro and Pro Max were at 43.8°C and 43.2°C, respectively. The iPhone Duo had a 20% lower frame rate than the iPhone 18 Pro models and couldn’t maintain 300 nits of brightness, dropping to 185 nits.
9to5Mac said that the iPhone Duo “runs a little hotter than the iPhone 18 Pro, but not enough to impact performance.” Tom’s guide ran a benchmark thermal test and found that the iPhone Duo was able to spread heat evenly across the entire body of the device, but it was a few degrees warmer than the Galaxy Z Fold8 that the site compared it to. The iPhone Duo achieved a stability score of 75.9% in the 3DMark stress test, compared to 79% for the iPhone 18 Pro Max and 72% for the Z Fold8.
Gizmodo didn’t find heat to be an issue, stating that the vapor chamber “does a great job cooling it to avoid lags or slowdowns” when apps use “all CPU and GPU cores.”
The iPhone Duo launches this Friday, so we won’t have to wait long to see if heat will be an issue for the everyday user.
