Wondering if thermal paste is necessary for your CPU or GPU and which type to use or avoid? We’ve got you covered!
If you’ve ever changed or installed a CPU in your computer, you’re probably familiar with thermal paste – the thick “goop” between the CPU case and its heat sink.
This guide will tell you everything you need to know about how thermal paste works, why it matters, and how to choose the right type.
We’ll also present some tips for choosing the right thermal paste, as there are some significant differences between the various types.
Does Thermal Paste Matter?
As a general rule, thermal paste should always be used on a CPU or GPU. It is cheap, easy to apply, and can make more than a 60% difference in heavy-load temperatures. CPU’s and GPU’s with pre-applied paste should be inspected, but additional thermal paste isn’t required if the existing paste is satisfactory.
That’s the quick, too-short answer. Not all types of thermal pastes are equal and there are some important caveats, so we need to dig a little deeper into the details.
Thermal paste, also called thermal compound, thermal grease, thermal interface material (TIM), thermal gel, heat paste, heat sink compound, heat sink paste or CPU grease, greatly increases the thermal conductivity of the CPU-to-heat sink interface.
The thermal conductivity of most thermal pastes is up to 100 times greater than air. For this reason, applying a layer of thermal paste between the CPU (or GPU) and heat sink is always recommended, whether or not fans are present.
Tests have been conducted on CPU’s with and without thermal paste applied. When the computer is idling (not performing any significant amount of computation) there is relatively little difference in CPU temperature.
For example, a typical CPU “idle” temperature may be 22C (71.6F) with paste and 28C (82.4F) without paste. This is noticeable but not particularly hazardous to the CPU.
However, when the CPU is at 100% load (working as hard as it can), the situation changes dramatically.
With thermal paste, a typical CPU temperature under 100% load might be 56C (132.8F); without thermal paste that temperature skyrockets to 94C (201.2F)!
While recommended operating temperatures vary depending on the CPU, the general recommendation is that your CPU temperature should not exceed 80C (176F). Therefore, not using thermal paste will likely prove to be quite destructive over time.
Again: Since the cost and time required to apply thermal paste is negligible compared to the cost of replacing a CPU or GPU, it’s highly recommended to always use thermal paste.
Types of Thermal Paste
Metal-based thermal pastes have the highest thermal conductivity and therefore the best performance.
One drawback to metal-based pastes is that they are also electrically conductive, so if you’re not careful in applying them they can potentially short-circuit pins on the CPU or other electrical connections on your motherboard.
A subset of metal-based pastes is “liquid metal” pastes, which flow more readily and have even higher thermal conductivity.
Ceramic-based thermal pastes don’t contain any metal, so they are not electrically conductive. This makes them safer to use. Additionally, they are less expensive than metal-based pastes. For these reasons ceramic-based pastes are very popular.
The only drawback here is that ceramic-based thermal paste has a slightly lower thermal conductivity than metal-based pastes.
Silicone-based thermal pastes are typically pre applied to a thermal pad that goes between the CPU and heat sink. They aren’t as effective as metal or ceramic-based pastes so we won’t spend much time on them here.
Adhesive vs Non-Adhesive Pastes
The thermal pastes we’ve discussed gere are all non-adhesive, meaning they don’t physically bond one device to another. There are other compounds on the market, such as thermal epoxies, that form a permanent mechanical bond between devices.
Since it’s typically desirable to be able to remove the heat sink from the CPU, adhesive compounds are not recommended.
It’s not hard to imagine how having something permanently stuck to your CPU could potentially create some major problems when attempting maintenance in the future.
There are many, many choices available in thermal pastes, so much so that it may be a bit intimidating to choose one.
As mentioned, pastes have different thermal conductivity, but there are other factors to consider as well, such as the maximum temperature rating, viscosity, and density.
Viscosity refers to how “sticky” the paste is, which affects how well the heat sink will stick to the CPU. This is more of a personal preference than a performance metric.
Density refers to how well the paste will fill in the microscopic air gaps between the CPU and heat sink. A less dense paste, such as a liquid metal type, will fill in the gaps better but will also flow more easily over the surface of the CPU and possibly onto unwanted components or contacts on the motherboard.
There are generally three trade-offs to consider when evaluating a paste: cost, performance, and ease of use. Usually, any metal or liquid metal paste will have better performance but it may be higher cost and be harder to use properly. Conversely, ceramic pastes will be lower cost and easier to use, but they will have worse performance.
The way you intend to use your CPU can help you decide which paste is right for your needs. For instance, if you are an avid gamer, interested in overclocking, or someone who does video editing, you may be concerned with finding a paste with a high thermal conductivity and low viscosity and density.
You may also be concerned with finding the highest maximum temperature rating possible. For any of these reasons, a metal-based paste might be the best fit.
On the other hand you may use your computer for less “CPU-intensive” tasks such as browsing the internet and creating business documents. In that case it might make more sense to look for a lower cost, user-friendly ceramic-based paste.
Our Recommended Best Thermal Pastes
Thermal Grizzly’s Kryonaut thermal paste is widely used and praised by a multitude of PC power-users and overclockers. It features nano-aluminum and zinc oxide components with a special carrier structure that keeps it from drying at high temperatures.
Arctic MX-4 thermal paste has become one of the top-selling pastes on the market. This compound is metal-free and non-electrically conductive. It’s a great choice for anyone looking for a paste with more long-term stability. Arctic advertises it as lasting for at least 8 years.
Widely used by enthusiasts and overclockers, Arctic Silver 5 is a hybrid thermal paste that contains 88% thermally conductive filler, micronized silver, sub-micron zing oxide, aluminum oxide, and boron nitride particles.
Noctua’s NT-H1 is a hybrid thermal paste that is also very popular with high-performance PC builders. It’s easy to apply and runs well at high temperatures.
Cooler Master’s High Performance Thermal paste contains metal oxides and resists changes in consistency up to 177°c with low bleed.
How Heat Damages Your PC
The reason that all computers use some combination of fans, heat sinks, and thermal paste comes down to the inescapable fact that electronic devices generate heat. CPU’s (& GPU’s), in particular, generate a lot of heat.
To understand why things get so hot, it’s important to understand that CPU’s are comprised mostly of one thing: transistors. At the most basic level, a CPU works by turning transistors on and off. While a transistor is on, it conducts electricity; while it’s off, it doesn’t. In both of these states, the amount of heat generated is relatively insignificant.
The problem comes in the transition from “on” to “off”. When the flow of electric current is suddenly interrupted, much of its energy is dissipated as heat. When you consider that a typical CPU may be comprised of 100 million transistors or more, the scale of the problem becomes apparent.
With that many transistors all turning on and off at billions of times per second, a lot of heat is generated. If some of that heat is not directed out of the CPU, it will quickly rise to levels that destroy the CPU.
This “self-destructive” amount of heat is why all CPU’s require a large heat sink to be physically attached. The function of the heat sink is to transfer heat from the CPU to the air where it is then removed from the CPU case via fans.
Typically, the heat sink will “lock on” to the CPU via mechanical clips, screws, or some other fasteners on the motherboard or CPU socket. This mechanical coupling only goes so far in transferring heat from the CPU to the heat sink though, because of microscopic imperfections in the surface of both the heat sink and the CPU case. These tiny imperfections can be thought of as “air gaps” between the two devices.
Before proceeding, we need to define an important term: thermal conductivity. The thermal conductivity of a material refers to its ability to conduct heat.
Materials like metal have a high thermal conductivity, which explains why the handle of a metal pan on the stove gets so hot. Air, on the other hand, has a relatively poor thermal conductivity as compared to metal.
Our CPU case and heat sink are made of metal, specifically copper, so they conduct heat well, but any air in between them will inhibit the flow of heat.
In other words, the thermal conductivity of our system is only as good as the part of it with the worst thermal conductivity. Therefore, if we can fill in the tiny air gaps between the CPU and heat sink with some material that’s more thermally conductive, we’ll greatly improve our ability to move heat out of the CPU and into the heat sink.
This is where thermal paste comes in.
Hopefully this article has convinced you of the importance of using thermal paste.
If the surfaces of your CPU case and heat sink were perfectly flat, there would be no microscopic air gaps to degrade the thermal conductivity of your system, but unfortunately such perfection is not physically possible.
The best way to ensure adequate heat transfer from your CPU to the heat sink is to always use a quality thermal paste.
Additionally, you should now have a good idea of what characteristics to look for in a paste, depending on what kind of user you are- Liquid metal types are preferred by “power users” who run their CPU’s at higher temperatures, while ceramic types may be a better fit for everyone else.
While performance and usability characteristics do vary, any paste you choose will greatly aid in keeping your CPU cool and extending its life.