Apple announced a redesigned thermal system for the iPhone 18 Pro and iPhone 18 Pro Max, featuring a next-generation vapor chamber with three times the surface area of the one in the iPhone 17 Pro. The new chamber constantly cycles deionized water to improve cooling performance, allowing the A20 Pro chip to sustain higher performance for longer under heavy workloads.

Apple also redesigned the silicon packaging, using "custom packaging inspired by our M-series chips." This places the silicon die and memory side by side rather than stacked, removing the memory from the chip's thermal path and letting the A20 Pro connect directly to the vapor chamber.

According to Apple, the combination of the new packaging, new thermal materials, and the larger vapor chamber delivers up to a 40% gain in sustained performance over the previous generation, which the company calls the highest sustained performance yet in an iPhone.

This design essentially creates a mini version of Earth's water cycle inside the phone: water in the chamber evaporates when hot and moves to another part, then condenses and cycles back, ensuring reliable cooling.