Several iPhone Duo reviews covered the device’s thermal properties, and reviewers’ opinions varied. Some thought it was just hot, while others thought it was too hot at times.
Joanna Stern said the back of the device gets hot when using FaceTime and taking photos. She had to end a FaceTime call during testing because it was too hot. “Yeah, I’m going to burn my hand,” she said. “This thing is getting really hot.”
Apple told him the heat was a sign that the iPhone Duo’s thermal design was directing heat away from the chip to maintain performance. “But to me, it feels like the phone is really hot,” she 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 pipe in the hinge to transfer heat between the two halves, providing more surface area for heat dissipation.
The edge said that the iPhone Duo heats up during prolonged camera use, especially if both screens are on for features like Duo Preview. “You can just feel the phone getting a lot hotter when this happens,” the review reads. “The phone gets hot enough that it starts to lag after a while.” The site also said that it gets hot when running third-party apps, especially video apps and Google apps.
PetaPixelThe review unit got warm when gaming, photo editing, or any activity that uses the processor, with the heat felt on the right side of the unfolded device.
Mrwhosetheboss performed 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 iPhone Duo’s performance was lower than the iPhone 18 Pro Max. When open, the iPhone Duo has a large, high-resolution screen 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 “massively” 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 it couldn’t maintain a brightness of 300 nits, dropping to 185 nits.
9to5Mac said that the iPhone Duo “runs a little hotter than the iPhone 18 Pro, but not in a way that impacts performance.” Tom’s guide ran a benchmark thermal test and found that the iPhone Duo was able to distribute heat evenly across the entire body of the device, but it was a few degrees warmer than the Galaxy Z Fold8 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 a problem, saying the vapor chamber “does a solid job of cooling it to prevent any lag or slowdown” when applications use “all CPU and GPU cores.”
The iPhone Duo launches this Friday, so we don’t have long to wait to see if heat will be an issue for the everyday user.
Gn tech
