What is CPU/GPU Thermal Paste Made of?

Thermal paste is used in every single computer around the world, yet many people still don’t know exactly what it’s made of. In this article, we’ll dive deep into the various possible compositions of thermal pastes.

Different types of thermal paste

For anyone who hasn’t applied thermal paste often, it might be a shock to learn that there is more than one type of thermal paste. Yes! There are several types of thermal pastes and new ones are being developed every day. Before we go through them, let’s review the components of most thermal pastes.

Thermal paste serves 2 roles – to be thermally conductive and to be a gap-filler for the microscopic spaces between the CPU and the heatsink. To serve these roles, it should be greasy or liquid and be – you guessed it – thermally conductive. To that end, most thermal pastes consist of a liquid matrix and a thermal-conductive filler. By changing the types of substances that fill these roles (no pun intended), we can create different types of thermal pastes with different properties. We can vary the viscosity, the thermal conductivity, and other properties.

So what are the main types of thermal pastes?

Silicone-Based

Silicone-based thermal pastes use a silicone liquid matrix to hold a thermally conductive metal-oxide filler in place. Silicone-based thermal pastes are amongst the most common thermal pastes on the market and are often found pre-applied in ready-made PC’s and laptops.

And for good reason – they’re a jack of all trades.

Because they use silicone, they’re very viscous which makes them easy to spread evenly onto a CPU or GPU and not prone to leak. They have excellent thermal conductivity and, unlike other thermal pastes, are not electrically conductive. So even if there is a leak, you can clean up and move on.

Carbon-Based

Carbon-based thermal pastes are similar to silicone-based, but instead of metal oxide fillers, they instead use carbon nano-particles to help conduct heat. They have about the same viscosity and thermal conductivity as silicone-based thermal pastes.

But the biggest advantage to using these is their electrical conductivity – or rather lack thereof. Because these pastes don’t use any metal particles, there’s no chance that they would carry a charge from any source. Technically-speaking, they are the safest to use in a computer or on any processor that is in close quarters with other components.

Liquid Metal-Based

Liquid metal-based thermal pastes are a little different from the other two we’ve explored so far. Unlike silicone-based and carbon-based thermal pastes, liquid metal-based thermal pastes don’t technically have a liquid matrix or a filler. Instead, the liquid metal acts as both the matrix and the filler. Because it is metal, it can conduct heat very well, and because it is liquid, it can naturally act as a gap-filler. Liquid metal-based thermal pastes clock some of the highest thermal conductivity ratings and are popular in high-end builds where overclocking is as natural as breathing air.

This may all sound perfect. So why doesn’t everyone just use liquid metal-based thermal pastes?

Well, in addition to being thermally-conductive, they are also electrically-conductive. Recall from that one time you touched a doorknob and it zapped your finger – metal can carry charge. A thermal paste made entirely of metal acts the same way as that knob. And usually this would be fine, but a computer is a machine with very specific pathways for every charge. If a single drop of liquid metal-based thermal paste gets on any component in a computer, it could short-circuit the machine and render it a giant paperweight.

Yeah. Not for the faint of heart.

If that wasn’t bad enough, most liquid metal-based thermal pastes consist of gallium. If gallium touches aluminum, it forms an alloy which crumbles at the touch.

Phase Change Materials

Lastly phase change materials. Phase-change materials are the black sheep of the family in that, strictly speaking, they’re not technically “thermal paste”. They’re called phase change materials are PCM’s because they harness the power of an endothermic reaction which occurs when a substance changes states to cool its surrounding surfaces. A simple example of this is an “instant cold” pack that you might use if you get injured.

Phase change materials are a cocktail of chemicals with a melting point of around 70°C. So when the substances hits that point, the material begins to change phase (often solid→liquid or liquid→solid) and store heat energy within the endothermic reaction.

These are most commonly used for industrial applications.

Composition of silicone-based thermal paste

 As mentioned earlier, silicone-based thermal pastes are amongst the most common and most reliable of all thermal pastes. They consist of a liquid matrix (also sometimes called a base) and metal oxide fillers. Silicone itself is not thermally-conductive but it is viscous and allows the thermal paste to flow, fill gaps, adhere to surfaces, and hold other thermally-conductive compounds. It is sometimes called the “silicone oil base.”

The compounds inside the silicone base are usually metal oxides like zinc oxide. These compounds have a high electron mobility which means they can transfer energy quickly. Other metal oxides that are sometimes used in silicone-based thermal pastes include aluminum oxide, boron nitride, and aluminum nitride. These have mostly the same properties and function similarly as fillers.

Why we recommend using silicone thermal paste

Reading about all the different types of thermal pastes, may get you excited to try out some new ones – and you should! There are many different options and, depending on your goals, you may want one and not another. However, we personally recommend you use silicone-based thermal paste for 99% of all your projects.

Firstly, silicone-based thermal paste has the highest cost-performance ratio out of any other materials we’ve listed so far. It usually weighs in at ~$2/g, as compared to liquid-metal based at ~$8/g and phase change materials at ~$10/gram. To note, phase change materials are usually sold for industrial applications so the cost may be much higher in bulk.

Secondly, when compared to carbon-based thermal pastes, silicone-based thermal paste is more durable and long-lasting. This is because Silicone is made of Silicon (Si) and Oxygen. Silicon’s chemical stability is much higher than that of Carbon which allows it to withstand more heating and cooling cycles.

And lastly, as mentioned previously, silicone-based thermal paste has great thermal conductivity, no electrical conductivity, and is not toxic. Which makes it the safest choice.

Our Kooling Monster KOLD-01 is a silicone-based thermal paste with the exact properties described above. It’s long-lasting, effective, and guaranteed to make your PC run at its absolute best.

Other thermal paste alternatives

In case you really have it out for thermal pastes, there are other alternatives you can try. Thermal pads are solid pieces of material which can be cut to the size of your CPU. They provide decent thermal conductivity at higher temperatures, but are not great gap-fillers. Thermal gel is another alternative. Thermal gel solidifies when exposed to air, making it last longer but also complicating the application process. Read more about thermal paste alternatives in our article here.

There are many different thermal paste brands with their own different colors and branding, but what you should remember is that they mostly all fall into the categories of either silicone-based, carbon-based or liquid metal-based. If you choose to go with liquid metal-based thermal paste, make sure to take proper precautions as it is electrically conductive. If you choose to go with carbon-based thermal paste, remember when you apply it – because it may not last as long and will need to be actively reapplied. And if you choose to go with silicone-based thermal paste, remember to use the best on the market – Kooling Monster KOLD-01!