How iPhones stay cool: heat spreaders and vapor chambers
Why a phone gets warm
The CPU, GPU and other components consume electrical energy, some of which becomes heat. The iPhone Pro Max models discussed here have no fan; cooling is passive. It moves heat away from hot components to a larger surface, from which heat escapes into the surroundings.
Conventional heat spreading
Heat travels through contact materials, metal parts and the internal structure towards the body. Thin heat-spreading layers, including graphite in smartphone designs, distribute it over a larger area. These are not ‘graphite rods’ or a pump. The exact layers vary by model; ‘standard’ in our table is shorthand, not an absence of cooling.
iPhone 15 and 16 Pro Max: internal structure
In iPhone 15 Pro, the outer titanium band is bonded to an internal aluminum structure that Apple describes as helping dissipate heat. Documentation for iPhone 16 Pro identifies an aluminum internal frame and thermal substructure. Cooling therefore cannot be judged by the exterior metal alone; the whole structure carries heat.
iPhone 17 Pro Max: vapor chamber
Apple uses a sealed vapor chamber containing deionized water, laser-welded into the aluminum body. A vapor chamber transfers heat as liquid evaporates near a hot area and condenses in a cooler region. Liquid returns within the closed system; there is no need for the user to refill it. Heat then spreads through the body.
What this means for games
The main benefit is sustaining performance for longer under load. When too hot, a phone may reduce performance, brightness or charging speed to protect its components. Better heat spreading does not guarantee a cold body: the body can feel warm precisely because it is receiving heat from the chip.
Can we say ‘40% better cooling’?
Not without comparable temperature tests. Apple’s ‘up to 40%’ claim for iPhone 17 Pro concerns sustained performance from the chip and new system together, not a 40% temperature reduction. Chamber size cannot be converted directly into cooling efficiency either. Our table shows the design type, not an invented efficiency percentage.
How to help your phone stay cool
Avoid direct sunlight and demanding games while charging in a hot room. If a temperature warning appears, stop the workload and let the device cool somewhere cooler. Do not put it in a refrigerator; sudden temperature changes and moisture can cause harm.