Apple says iPhone 15 Pro running warm is "expected behavior", exploring graphene solution for iPhone 16 Pro

While we are reasonably confident Apple has overcome the overheating concerns raised in relation to the iPhone 15 Pro and iPhone 15 Pro Max at launch, thermal concerns persist. We have noticed that our iPhone 15 Pro Max continues to run warmer than we have experienced other iPhones run in the past. Indeed, just about any other phone with the exception of the Pixel 8 Pro. 

We recently visited an Apple Store as a private customer to have our iPhone 15 Pro Max tested for any faults, but all the tests the iPhone technician ran came back clear. So we pushed the technician a little more about how unusually warm we felt that this generation of Pro iPhone ran compared to previous models we’ve used. Somewhat to our surprise, the technician quietly admitted that internally, Apple has advised its technicians that this is to be considered “expected behavior”.

While it is not a major issue in the way that the whole overheating saga that marred its launch, it still feels unusual to have a device running warm when you are not actually doing anything with it other than carry it around with you. As Apple analyst Ming Chi-Kuo highlighted, titanium is less heat conductive than the steel frame Apple had previously used on the iPhone 14 Pro series, and that this could at least be contributing to the thermal issues.

Apple soon acknowledged a software bug in iOS 17 was to blame for the overheating issues at launch, along with certain third-party apps that also caused the chip to overload and run hot. However, while the initial patch to address the issue helped to mitigate the problem, some users continued to have issues. Apple's most recent update, iOS 17.3, seems to have further helped with reducing the thermal issues we have experienced with our iPhone 15 Pro Max, but not stopped it from running warmer than we'd like.

Highlighting this, we tested our iPhone 15 Pro Max, Galaxy S24 Ultra, an iPhone 13 Pro, and the ROG Phone 8 Pro, all while idling at an ambient room temperature of 26-degrees Celsius for this article. The iPhone 15 Pro measured at 31.5-degrees Celsius, the Galaxy S24 Ultra at 29.3-degrees, iPhone 13 Pro at 28.7-degrees, the ROG Phone 8 Pro at just 26.8-degrees. Although the S24 Ultra is also made with a titanium frame, it is fitted with a vapor chamber that is 92% larger than the S23 Ultra to help offset the impacts of using titanium instead of the more conductive “aluminum armor” as it used for the previous model.

As a phone made specially for mobile gaming, it comes as no surprise to see the ROG noticeably cooler at idle. It uses a sophisticated combination of a graphite sheet, rapid-cooling conductor, boron nitride, vapor chamber followed by an additional layer of graphite. Unsurprisingly, its sustained performance also blows away the iPhone and the S24 Ultra. But it is also clear that the iPhone 15 Pro runs considerably warmer at idle than all the phones here, including the iPhone 13 Pro. But apparently Apple has a fix, but iPhone 15 Pro users won’t be able to benefit from it.

Apple had been rumored to be testing iPhones with vapor chambers as far back as 2021. However, we are yet to see Apple employ such a method which would certainly have aided both the iPhone 15 Pro and the iPhone 14 Pro series, which also suffered from thermal issues, but only under intensive load when playing games, for example. A fresh rumor has also surfaced that in addition to a new steel outer coating for the iPhone 16 Pro batteries, Apple could also be looking to introduce the use of graphene as a thermal solution for the iPhone 16 Pro too.

Rutgers researchers highlighted a study published in 2017 that showed them applying a graphene layer directly attached to the silicon could be a more effective method than traditional solutions like graphite, as it has much greater thermal conductivity. This would help whip away heat from the chip and dissipate it more effectively. Using this approach instead of a vapor chamber could be favored by Apple as it wouldn’t add any additional weight to the iPhone 16 Pro. Apple is also said to be considering a steel casing for the iPhone 16 Pro battery to further dissipate heat.

Whatever approach Apple adopts to keep thermals in check for the iPhone 16 Pro series will most certainly be welcome. With thermals still posing issues on both the iPhone 14 Pro and iPhone 15 Pro, the next iPhone Pro due later this year might finally put this problem to bed.