What Does Thermal Paste Do?

In this post, we discuss what thermal paste is, what it does, and what the different types of thermal pastes are.

You’d be forgiven for thinking that thermal paste isn’t all that important. Compared to the other components of a computer—most of which have hunks of metal attached to them, or delicate looking circuitry—thermal paste is a simple, unassuming tube of gray… well, paste.

Despite its simple appearance, thermal paste is vital to the longevity of your system—of the CPU in particular.

As such, it begs the question: What exactly does thermal paste do?

What is Thermal Paste and What Does it Do?

If you Google that question, you’ll probably end up with a cookie cutter answer: Thermal paste increases the thermal conductivity between the CPU and its cooler—both AIOs and air coolers.

But what does that mean? In reality, thermal paste works with two other components of the computer—the CPU’s Integrated Heat Spreader (IHS)—and the baseplate of the cooler, whether it’s an AIO or an air cooler.

When looking at a CPU that’s been properly seated, it just looks like a square of metal. But that piece of metal isn’t actually a part of the CPU—it’s the IHS. In tandem with the CPU cooler and thermal paste, it keeps the CPU cool.

When a CPU is operational, it generates a massive amount of heat. While the amount of heat generated varies greatly, depending on how hard it’s being pushed from moment to moment, it typically idles at 40-44 ℃. Under load, it can go as high as 85-90 ℃—almost hot enough to boil water.

Safe CPU Temps: How Hot Should My CPU Be?

If all that heat were to gather in one area, the CPU would damage itself, to the point of degrading or becoming completely unusable. Most modern CPUs have safety measures to prevent that nowadays—when certain temperature thresholds are reached, they lower their performance to lower temperatures as well.

This means that if the CPU is to perform optimally, it needs to remain cool. It’s why the contact part of CPU coolers are (typically) made of metal—it’s an excellent conductor of heat.

The heat generated by the CPU is absorbed by the IHS, then transferred to the metal part of the cooler—and, then the cooler dissipates that heat into the surrounding air within the case, where the computer’s case fans can then exhaust the air out of the case.

In the case of an AIO cooler, the contact part of the cooler transfers heat to the water within the tubing. As the water is pumped through the radiator, the heat is transferred to the radiator, diffused, and cooled by the attached fans.

Neither of these things would work without thermal paste. While metal is an excellent conductor of heat, air is the exact opposite. But why is that relevant?

What Thermal Paste Does

When looking at the contact part of a cooler, it might appear to be perfectly smooth—but it’s not. No matter how metal is treated, no matter what method is used to shape and smooth it, there are imperfections. Molecular grooves and nicks exist that can’t be seen under normal circumstances.

These imperfections fill up with air when a cooler is placed on the CPU. Not only does this greatly reduce the amount of contact between the IHS and the radiator, air is not thermally conductive. This results in greater amounts of heat remaining on the IHS. That’s where thermal paste steps in.

Thermal paste is sort of a mishmash of different materials—most of which conduct heat. Thermal paste fills in those invisible gaps between the IHS and the cooler, increasing the points of contact, and in turn increasing the amount of heat transferred between the IHS and the CPU cooler.

Types of Thermal Paste

That said, while all thermal paste performs the same role, not all of it is composed of the same material, and as such, not all of it shows the same level of performance. Broadly speaking, there’s five different types of thermal paste—one of which isn’t really a paste at all:

1. Silicon
2. Ceramic
3. Carbon
4. Metal
5. Liquid Metal

Silicon and Ceramic-based thermal pastes are usually what you’ll find pre-applied to coolers. While the quality of these pastes may vary from brand to brand, they’re usually similar enough in performance that it’s not worth removing the pre-applied paste—-unless you’re doing some serious overclocking.

Carbon-based thermal paste is the next “step up” from silicon and ceramic, so to speak. It’s composed of small carbon fibers, and often contains diamond powder—keeping heat conductivityhigh, while providing even better insulation against electricity. The Arctic MX4 is slightly more expensive than other options at $15 per tube, but performs noticeably better than its silicon and carbon based counterparts.

The next two on the list, as the name suggests, are thermal pastes composed primarily of metal compounds. While they yield even greater performance than the aforementioned types, unlike them, metal-based pastes are electrically conductive, as well as thermally conductive. This means that if applied improperly, it can and will short circuit components of the computer. Research properly before trying to apply either of them.

Conclusion

Ultimately, thermal paste helps fill in the air pockets that form between your CPU’s heat spreader and the baseplate of your CPU cooler. Without thermal paste, your CPU would not be able to transfer heat to your CPU cooler in an efficient manner, thus resulting in overheating and system shutdown.