Multiple early reviews found mixed results on whether the iPhone Duo runs hot: some testers described it as merely warm, while others reported it became uncomfortably hot during sustained tasks.
The most dramatic anecdote came from reviewer Joanna Stern, who said the back of the device got warm while using FaceTime and taking photos and that she had to end a FaceTime call during testing because it got too hot. “Yeah, I’m gonna burn my hand off,” she said. Apple told her the warmth was a sign of the iPhone Duo’s thermal design moving heat away from the chip to keep performance up, but Stern added, “But to me, it just feels like the phone is really warm.”
iPhone Duo thermal design and specs
The iPhone Duo uses the same custom vapor chamber setup and the A20 Pro chip found in the iPhone 18 Pro, although its vapor chamber is thinner. Apple also added a flexible graphite pipe in the hinge to transfer heat between the two halves and increase surface area for dissipation.
Several hands-on reports and tests found heating during sustained, processor-heavy activities. Long camera use—especially with both displays active for features like Duo Preview—was repeatedly mentioned as a scenario that makes the device noticeably hotter and, in some cases, causes performance lag. Third-party video apps and certain apps from Google were also singled out as contributors to increased heat in some tests.
Independent stress and gaming tests showed measurable differences versus other recent models. In a 20-minute stress comparison, one tester found the iPhone Duo trapped heat when closed and delivered lower performance than the iPhone 18 Pro Max; with the device open, the large high-resolution display also affected performance, though the tester said the difference in daily use was not “massively” noticeable. A 30-minute gaming test recorded temperatures of 46.5°C for the iPhone Duo, versus 43.8°C for the iPhone 18 Pro and 43.2°C for the iPhone 18 Pro Max. In that test the Duo posted a roughly 20 percent lower frame rate than the 18 Pro models and could not maintain 300 nits of brightness, dropping to 185 nits.
Benchmarking also produced mixed signals on stability and heat spread. In a 3DMark stress test the iPhone Duo scored a 75.9 percent stability score, compared with 79 percent for the iPhone 18 Pro Max and 72 percent for the Galaxy Z Fold8. One benchmarked comparison noted the Duo spreads heat evenly across its body but runs a few degrees hotter than the Z Fold8.
Not all conclusions were negative: some reviewers reported that the vapor chamber and thermal design prevented significant lag or slowdown even when apps used all CPU and GPU cores, and one summary assessment described the Duo as running a bit hotter than the iPhone 18 Pro but not in a way that impacted performance for that reviewer.
The iPhone Duo launches this Friday, leaving only a short time before wider real-world use will determine how noticeable these heat issues are for typical users.
