Would increasing the size of the cooling system actually cause a phone to lag? Preliminary tests of the Samsung Galaxy S25 FE would appear to validate just that, the handset throttling more than the previous generation even though hardware is virtually the same and the vapor chamber 13% larger.
On paper, the S25 FE should have a thermal advantage. It ships with the Exynos 2400 the same 10-core CPU and Samsung Xclipse 940 GPU found in the mainline Galaxy S24 and only a slight bump in the prime Cortex-X4 core’s clock speed over the S24 FE’s Exynos 2400e. Both chips are built on Samsung’s 4nm process, and both GPUs run at 1,095 MHz. Yet in GPU stress testing, the S25 FE maintained just 59% to 66% of peak performance, compared to the S24 FE’s steadier 71% to 72%.
That drop in sustained performance is especially puzzling given Samsung’s hardware claims. The S25 FE’s vapor chamber is not only larger but also uses a liquid thermal interface to improve heat transfer. Vapor chambers operate on a closed-loop phase-change cycle: heat from the SoC vaporizes an internal liquid, the vapor travels to cooler areas of the chamber, condenses, and releases heat into the phone’s frame before the liquid returns to repeat the process. In theory, a larger chamber should increase the surface area for heat dissipation, lowering internal temperatures and delaying thermal throttling.
But just as was seen in comparative thermal tests of other vapor-cooled devices, by the size of the chamber alone does not always give the best results. Choice of material, wicking construction on the inside, and integration into the body all have effects upon efficiency. Oversized vapor chambers have corresponding graphite stacks to spread the heat more evenly, for example, on gaming-geared smartphones like the ASUS ROG Phone 6, or multi-level cooling stacks are implemented or even active fans are used to sustain optimum results.
For the case of the S25 FE, there are two possibilities. First, firmware. Early thermal profiles for Samsung might be too cautious and trigger GPU downclocking sooner than necessary to protect components. That would be like the earlier Exynos 2400 action, where CPU throttling began within minutes of sustained load, but real-world responsiveness remained superb. Firmware updates, however, are capable of moving these thresholds, and this has happened once before within the debut of the Galaxy.
The other alternative is the real-world performance of the vapor chamber falls short. If the wicking layer on the inside isn’t properly tuned, or the chamber-to-SoC package contact isn’t optimal, the efficiency of transferring the heat falls even as the footprint gets increased. Sporadic liquid flow within the chamber can create localized hot spots, causing the system-on-chip to throttle earlier.
Stress test methodology also points to the issue. Tests constrained by the GPU, such as 3DMark Wild Life Extreme, run contiguous high-load loops to simulate long gaming scenarios, where thermal saturation happens. For properly optimized configurations such as the dual-layer vapor chamber of the Red Magic Astra tablet the performance stability level can be well beyond 88%, even under extreme loads. In the S25 FE, the sub-66% level of stability means the cooling system enters thermal limits early and the firmware makes clock reductions to prevent heat breakdown.
Compounding the disappointment, real-world gaming tests mirror the synthetic results. Reviewers noted that both the S25 FE and S24 FE grew warm after 15–20 minutes of titles like Diablo Immortal, but the S25 FE showed no perceptible improvement in surface comfort despite its bigger chamber. This is critical for mobile gamers, as high external temperatures can make a device uncomfortable to hold, while high internal temperatures degrade sustained frame rates and, over time, battery health. The Exynos 2400 chip itself remains a capable processor, touting GPU scores on or even above Qualcomm’s Adreno 750 in certain ray tracing tests and 5G modem speeds ahead of what you would anticipate. However, without satisfactory thermal management, those benefits are harder to maintain through longer workloads. Whether Samsung can fix the S25 FE’s throttling through firmware tweaks or hardware adjustments remains the key question remains the key to this “Fan Edition” actually living the label for energy-conscious consumers.
