Multiple iPhone Duo reviews covered the device's thermal properties, and reviewer opinions varied. Some found that it was just warm, while others thought it was running too hot at times.

Joanna Stern said the back of the device got warm when using FaceTime and taking photos. She had to end a ‌FaceTime‌ call during testing because it got too hot. "Yeah, I'm gonna burn my hand off," she said. "This thing is getting really warm."

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 to me, it just feels like the phone is really warm," 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 .…