Cold can on the back of an iPhone 18 Pro boosts its sustained benchmark

Software developer Matt Birchler has found a simple remedy for the iPhone 18 Pro losing performance under sustained load: laying a cold can of sparkling water on the back of the phone. He described the experiment in a blog post, and The Register reported the results on September 24.

A vapor chamber with three times the area

The most notable hardware upgrade in Apple's new flagship is its vapor chamber, which covers three times the surface area of the one introduced with the iPhone 17 Pro series. Such chambers are sealed metal units placed beside the processor: a tiny amount of water evaporates above the hot spot, the vapour moves to cooler areas and condenses, and a wicking structure carries the liquid back so the cycle can repeat.

Birchler ran a benchmark built into Quick Subtitles, the audio transcription app he develops, 20 times on an iPhone 18 Pro, an iPhone 17 Pro and an M4 Pro MacBook Pro, using Apple's on-device transcription model. The 18 Pro ranged between 447.9 and 320.9 words per second, a 50 percent jump over the 17 Pro. It also ran warmer, and once it started to heat up it did so faster than the older phone, which is exactly what a larger vapor chamber should do: pull more heat off the chip and spread it over a wider area.

The cold can test

Over the 20 runs the 17 Pro was throttled less than the 18 Pro, so Birchler attacked the heat from the outside. He took a cold can of La Croix out of the fridge, started a new benchmark run and set the can on the back of the phone. The numbers barely moved: the first run managed 429.9 words per second, and the twentieth still reached 400.4.

iOS thermal states tell the same story. Developers can see whether a device is nominal, fair, serious or critical; without the can the 18 Pro sat in the serious zone for roughly half of the runs, while with the can it never rose above fair. The Register estimates that, if the effect carries over to other workloads, the same work gets done about 14 percent faster.

Chips that are cooled passively

"It's clearly doing what it's supposed to do," Birchler told The Register. "Chips that are passively cooled will always have some level of throttling, so it's good to see progress here." For anyone willing to try the trick, his advice is simpler: "When they call you crazy, you turn around and tell them they don't know what they're missing."