What Is Thermal Paste? What It Does and Why Your CPU Needs It

Thermal paste is a heat-conducting compound spread between a CPU and its cooler that fills microscopic air gaps, so heat moves into the cooler instead of getting trapped.

Last updated: September 2026

It’s a few cents’ worth of grey goo, and your CPU can’t run properly without it. Thermal paste (also called thermal compound, thermal grease or TIM, short for thermal interface material) sits between the metal lid of your processor and the base of your cooler. Its only job is to get heat from one to the other as efficiently as possible.

This guide explains what thermal paste does, why it’s necessary, whether your CPU or cooler already comes with some, and what the different types are. If you already know all that and just want to buy some, skip to our best thermal paste guide.

What Does Thermal Paste Do?

Your CPU’s lid (the integrated heat spreader, or IHS) and your cooler’s base both look flat. Under a microscope, they aren’t. Both surfaces are covered in tiny ridges and dips, so when you press them together, they only touch at the high points. Everything in between fills with air.

Air is a very poor conductor of heat. Its thermal conductivity is roughly 0.026 W/m·K at room temperature. Thermal paste is far better than air, and when it fills those gaps, heat can flow from the CPU into the cooler across the whole contact area instead of just the high spots.

One thing paste is not: a replacement for good contact. Metal touching metal conducts heat much better than paste does. That’s why you only want a thin layer that fills the gaps. A thick blob pushes the cooler away from the CPU and makes temperatures worse, not better.

Is Thermal Paste Necessary?

Yes. Without it, the cooler only touches the CPU at scattered points, and heat builds up faster than the cooler can remove it. Modern CPUs protect themselves by slowing down when they get too hot. That limit, called Tjmax, is 100°C on Intel’s 13th and 14th Gen Core chips, 105°C on Intel Core Ultra 200S (Arrow Lake), and 95°C on AMD Ryzen 7000 and 9000. A CPU without paste reaches that limit quickly under load and then throttles, losing performance.

You need paste:

• When you install a new cooler (unless it has paste pre-applied)
• Every time you remove and remount a cooler, even briefly, because the old layer is disturbed
• When old paste has dried out and temperatures have crept up over the years

If your CPU is already running hot, our guide to CPU overheating signs and fixes helps you work out whether paste is the problem or something else.

Do CPUs and Coolers Come With Thermal Paste?

This is one of the most common questions, and the answer depends on what’s in the box.

What you bought	Thermal paste included?
A CPU on its own	No. Processors never come with paste on the lid.
A boxed CPU with a stock cooler	Usually yes, pre-applied on the cooler’s base.
An aftermarket air cooler	Often pre-applied, or a small tube or syringe in the box. Check the listing.
An AIO liquid cooler	Almost always pre-applied on the pump block.
A prebuilt PC	Yes, already applied at the factory.

Pre-applied paste is fine for a first install. Leave it alone and mount the cooler as it is. The catch is that it’s single-use: once you take the cooler off, you need to clean it off and apply fresh paste. Many unlocked, high-end CPUs (Intel’s K-series and most higher-end Ryzen chips) ship without a cooler at all, so with those you’re relying on whatever comes with your cooler.

Installing a liquid cooler? Our guide to AIO coolers explains how the pump block and pre-applied paste fit together.

Types of Thermal Paste

Most thermal pastes are a carrier (usually silicone or a synthetic oil) filled with tiny particles that conduct heat. What those particles are made of decides most of the paste’s behavior.

Metal-oxide and ceramic pastes

The most common type. The filler is usually a metal oxide such as zinc oxide or aluminum oxide. They’re electrically non-conductive, so a smear on the socket area is messy but harmless, and they clean up easily with isopropyl alcohol. Most mainstream pastes from established brands fall into this category, and they’re the right choice for almost every build.

Carbon-based pastes

Use carbon particles (sometimes marketed as graphite or “carbon micro-particles”) as the filler. Several popular pastes use this approach. Many are non-conductive, but not all carbon compounds are, so check the manufacturer’s description before assuming.

Phase-change pads

A solid sheet that softens and spreads once the CPU heats up. No syringe, no spreading, and no application mistakes. They’re popular for laptops and small builds, and they tend to hold up well over many heat cycles. The downside is cost per use and a bit more effort to clean off.

Liquid metal

A gallium-based alloy that conducts heat much better than any paste. It’s also electrically conductive, so a stray drop on the motherboard can short components, and gallium reacts with aluminum. Thermal Grizzly, which makes one of the best-known liquid metals, warns it must never be used with aluminum coolers. It belongs on expert builds, delidded CPUs and some laptops from the factory, not on a first build. Our liquid metal vs. regular paste guide covers the trade-offs.

A note on W/m·K numbers

You’ll see pastes advertised with thermal conductivity ratings like 8.5 or 12.5 W/m·K. Those numbers come from each manufacturer’s own measurements and aren’t comparable across brands; some manufacturers have stopped publishing them for exactly that reason. For a fair comparison, look at independent tests on the same CPU and cooler. We explain this in more detail in our best thermal paste guide.

Thermal Paste vs. Thermal Pads

Paste is for surfaces that sit almost flush against each other, like a CPU and cooler. Thermal pads are thicker, soft sheets used where there’s a real physical gap, such as between a graphics card’s memory chips and its heatsink. They aren’t interchangeable. Paste can’t fill a millimeter-wide gap, and a pad on a CPU is far too thick. If you’re working on a graphics card, see our GPU repasting guide.

Does Thermal Paste Expire?

Yes, in two ways. Paste in the tube slowly dries out or separates, especially if it’s been opened. Paste on the CPU gradually loses effectiveness over years of heating and cooling. Most desktops don’t need new paste for several years; laptops, which run hotter in tighter spaces, often need it sooner. For the details, read how long thermal paste lasts and how often you should replace it.

Applying and Choosing Thermal Paste

Once you know what paste does, the practical questions are how much, how and which one. Each has its own guide:

• How to apply it: how to apply thermal paste the right way
• How much to use: how much thermal paste to use on a CPU
• Which pattern: dot, line or spread
• Removing old paste: how to remove thermal paste
• Which to buy: the best thermal paste

Frequently Asked Questions

What is thermal paste made of?

A carrier, usually silicone or a synthetic oil, filled with heat-conducting particles. Those are typically metal oxides such as zinc oxide or aluminum oxide, carbon particles, or in some premium pastes other fine powders. Liquid metal is different: it’s a gallium-based alloy with no carrier at all.

What does thermal paste do for a CPU?

It fills the microscopic air gaps between the CPU’s heat spreader and the cooler base. Air conducts heat poorly, so replacing it with paste lets heat flow into the cooler much more efficiently and keeps the CPU from overheating and throttling.

Do CPUs come with thermal paste?

The CPU itself never does. If the CPU comes with a stock cooler, that cooler usually has paste pre-applied. Many high-end CPUs ship without a cooler, so the paste comes with the cooler you buy separately.

Is thermal paste necessary?

Yes. Without it, the cooler only touches the CPU at a few points and the processor quickly reaches its temperature limit and throttles. Every cooler installation needs paste, either pre-applied or applied by you.

Is pre-applied thermal paste good enough?

For a first installation, yes. Pre-applied paste on stock and aftermarket coolers is designed to work out of the box. Just remember it’s single-use: if you remove the cooler, clean it off and apply fresh paste.

Is thermal paste electrically conductive?

Most standard pastes are not, which is why a small spill is harmless. Liquid metal is conductive, and some carbon-based compounds can be, so always check the product description.

Can I use toothpaste or another substitute instead of thermal paste?

No. Household substitutes aren’t designed for the job, and some dry out or leave residue that’s hard to remove. Thermal paste is cheap; use the real thing.

What’s the difference between thermal paste and thermal compound?

Nothing. Thermal paste, thermal compound, thermal grease and TIM all refer to the same kind of product.

The Bottom Line

Thermal paste fills the invisible gaps between your CPU and cooler so heat can escape. Every cooler install needs it, whether it’s pre-applied or from a tube, and a thin layer of a standard non-conductive paste is right for almost everyone. Save liquid metal for when you know exactly what you’re doing. When you’re ready to buy, start with our best thermal paste guide.