Short answer: use thermal paste on almost every CPU and GPU. It's cheap, safe and good enough that a better material rarely buys you more than a degree or two. Use thermal pads where the gap is too big or too uneven for paste, like GPU memory and VRMs. Use a phase-change pad such as PTM7950 in a laptop or GPU you don't want to open again. Use liquid metal only on a bare die (delidded CPU, direct-die cooler) with a copper or nickel-plated cooler, because it conducts electricity and destroys aluminum.
| Thermal paste | Thermal pad | Phase-change pad | Liquid metal | |
|---|---|---|---|---|
| Best for | CPUs and GPUs | VRAM, VRMs, uneven gaps | Laptops, GPUs, set and forget | Delidded and direct-die chips |
| Typical maker-stated rating | about 5 to 15 W/mK | about 3 to 17 W/mK | about 8.5 W/mK | about 40 to 80 W/mK |
| Typical layer | very thin | thick (0.5 to 3 mm) | very thin once melted | very thin |
| Conducts electricity | No (most) | No | No | Yes |
| Safe with aluminum | Yes | Yes | Yes | No |
| Pump-out over time | Some formulas | No | Very little | No |
| Difficulty | Easy | Easy, if the thickness is right | Easy, fiddly film | Hard |
What do all three actually do?
A CPU's metal lid and a cooler's base both look flat. Under a microscope they look like two mountain ranges pressed together. They only touch at the peaks, and the valleys fill with air.
Air is a terrible heat conductor, about 0.026 W/mK. Copper is around 400 W/mK. So the job of every thermal interface material is the same: push the air out of the valleys and fill them with something that moves heat better than air does.
Think of it as filling potholes in a road. Paste is asphalt poured into the holes. A pad is a rubber mat laid over a gap you can't fill any other way. Liquid metal is the best filler there is, but it's also the one that ruins the road if it spills onto the wrong surface.
How much this matters: in the simplified example further down, a 0.05 mm air gap under a 200 W cooler would add over 400°C across that tiny layer. The chip would throttle long before that. Any thermal interface material fixes most of the problem. Choosing between them fixes the last few degrees.
Why is the W/mK number on the box misleading?
W/mK (watts per meter-kelvin) is thermal conductivity: how easily heat passes through the material itself. It's the number every product page leads with, and it's the least reliable spec in the category.
- Makers test it differently. There's no single required test method. Two pastes both rated 12 W/mK may have been measured in different ways. ARCTIC doesn't publish a W/mK figure for its pastes at all, because it considers the industry's numbers inflated.
- Thickness matters as much as the rating. Heat has to cross the whole layer. A thicker layer resists more, however good the material. That's why a thin, even layer of average paste beats a thick blob of premium paste.
- Contact matters too. Real results also depend on how flat both surfaces are and how hard the cooler presses down. A spec sheet can't capture either.
Pads make point 2 obvious. A 12 W/mK pad at 1 mm thick is 20 times thicker than a typical 0.05 mm paste layer. Worked through the formula below, that pad has roughly 14 times the thermal resistance of an 8.5 W/mK paste. The pad has the higher rating and still does much worse. That's why pads go on memory chips, where the gap is big, and not on the CPU.
On every Consumercarts thermal paste page, we show the rating the maker states and leave it blank when the maker publishes nothing. The number is a rough guide, not a ranking.
How many degrees is the difference, really?
Here's a simplified worked example. The temperature drop across the interface layer is:
temperature drop = heat × layer thickness ÷ (conductivity × contact area)
Take a 0.05 mm layer of each material and two common setups:
- With a lid: a desktop CPU where heat spreads through the metal lid (the IHS, or integrated heat spreader) before it reaches the paste. That's 200 W over roughly 900 mm².
- Bare die: a delidded CPU or direct-die GPU, where the cooler sits on the silicon itself. That's 250 W over roughly 250 mm².
| Setup | Air gap (0.026 W/mK) | Paste (8.5 W/mK) | Premium paste (16 W/mK) | Liquid metal (73 W/mK) |
|---|---|---|---|---|
| With a lid, 200 W, 900 mm² | over 400°C | 1.3°C | 0.7°C | 0.15°C |
| Bare die, 250 W, 250 mm² | over 1,900°C | 5.9°C | 3.1°C | 0.7°C |
Three things stand out:
- With a lid, the material barely matters. The gap between ordinary paste and liquid metal is about a degree. The lid spreads the heat over a large area before it ever reaches the paste.
- On a bare die, it matters a lot more. The same heat goes through a much smaller area, so each square millimeter carries more of it. That's where liquid metal earns its risk. It's also why enthusiasts who delid a CPU nearly always use liquid metal under the lid.
- Premium paste sits in between. Going from an 8.5 to a 16 W/mK paste halves the drop in both setups. On a normal desktop CPU, that's under a degree.
This model ignores contact resistance and assumes a perfect layer, so real-world differences are usually larger than these figures. The ranking holds, though, and so does the lesson: area and thickness decide how much the material matters.
When is thermal paste the right choice?
Nearly always. Paste is a grease: tiny particles (metal oxide, ceramic, carbon or aluminum) suspended in a carrier. The cooler's mounting pressure squeezes it into a layer a fraction of a millimeter thick. Most modern pastes are non-conductive, so a smear on the socket is a cleanup job, not a dead board.
Where it works best: any desktop CPU with a lid, and any GPU die when you're repasting a graphics card.
Where it struggles: heat cycling. Chips that heat and cool fast and often (GPUs, laptops, consoles) can slowly squeeze thin paste out from under the cooler. This is called pump-out, and it shows up as temperatures creeping up over months. Thicker, more stable pastes resist it better. Pump-out is the real reason to pick one paste over another, not a 2 W/mK difference on the box.
When to replace it: when temperatures are 5 to 10°C higher than when the system was new at the same load, or any time you take the cooler off. There's no fixed schedule. Our guide to how often to replace thermal paste covers the signs, and how much thermal paste to apply covers the method.
Popular choices: Arctic MX-6 and Noctua NT-H2. Compare them in Arctic MX-6 vs Noctua NT-H2.
When do you need a thermal pad instead?
When the gap is too big or too uneven for paste. On a graphics card, the main GPU die sits a fraction of a millimeter from the cooler, but the memory chips and power stages (VRMs) around it sit lower. Paste can't bridge a 1 or 2 mm gap. A soft pad can, because it squashes to fill the space.
The thickness rule: the pad has to match the gap it replaces, and this is where most GPU repads go wrong.
- Too thin: the pad never touches the memory chip. The memory overheats while the GPU core looks fine.
- Too thick: the pad props the cooler up off the main die. Now the core overheats, even with fresh paste on it.
Measure the old pads with calipers before you take them off, or find the thickness list for your exact card model. When unsure, a softer pad that's slightly too thick is safer than a hard one, because it squashes further.
About pad ratings: a higher W/mK pad helps, but thickness and softness matter more. A soft pad that makes full contact beats a harder, higher-rated pad that doesn't.
Popular choices: Arctic TP-3, Gelid GP-Extreme and Fujipoly Extreme X-e. See how a pad and a paste compare in Arctic MX-6 vs Arctic TP-3.
What about phase-change pads like PTM7950?
These are the exception to "pads don't go on the CPU." Honeywell PTM7950 is a thin film that is solid at room temperature. At about 45°C, Honeywell's stated phase change temperature, it softens and flows like a very thick paste. It fills the valleys and thins down to a layer as thin as good paste. When the chip cools, it firms up again.
That cycle is why it resists pump-out so well. Honeywell rates it at 8.5 W/mK with a thermal impedance of 0.04°C·cm²/W. Impedance measures the whole layer, not just the material, so it's the more useful of the two figures here.
Where it shines: laptops, GPUs and consoles, anywhere you want to repaste once and not open the device again for years.
Where it doesn't add much: a desktop CPU with a lid. As the worked example shows, the lid already hides most material differences.
Watch out for:
- Fakes. Counterfeit PTM7950 is common, so buy from a known seller.
- The first run. It needs one warm-up past its melting point to settle, so temperatures can look slightly high on the very first boot.
Compare it with paste in Arctic MX-6 vs Honeywell PTM7950.
Is there a fourth option?
Yes: graphite and graphene sheets such as Thermal Grizzly KryoSheet and Carbonaut. They're thin solid sheets you cut to size.
Strengths: they never pump out or dry out, and they can be reused across many remounts. That makes them popular on test benches and on GPUs that get taken apart often.
The catch: they conduct electricity, so a stray flake or a sheet overhanging the die edge near small surface components can short them. They also need very flat surfaces and firm pressure to perform well.
Compare one against paste in Arctic MX-6 vs Thermal Grizzly KryoSheet.
When is liquid metal worth the risk?
Liquid metal is a gallium alloy that stays liquid at room temperature. Makers rate it roughly 5 to 10 times higher than paste: Thermal Grizzly Conductonaut at 73 W/mK, for example. It isn't only for enthusiasts, either. Sony uses liquid metal on the PS5's processor, and ASUS has shipped it in ROG gaming laptops since 2020.
It's worth it on a bare die: a delidded CPU, a direct-die frame, or a laptop or GPU die where every degree matters. On a normal desktop CPU with a lid, the gain is small and the risk is not.
Before you use it, check all five:
- The cooler's contact surface is copper or nickel-plated. Gallium attacks aluminum and eats into it. Never use liquid metal on an aluminum cold plate or heatsink.
- You'll insulate the components around the die. Liquid metal conducts electricity, and a single bead rolling onto the tiny capacitors next to a die can short them. Cover those with Kapton tape or a conformal coating first.
- You'll use very little. A thin, even film on both surfaces is enough. Excess is what escapes.
- You accept that bare copper will stain. Copper slowly absorbs some gallium. That leaves a gray stain and can thin the layer over months, so check temperatures after a few months. Nickel plating resists this.
- Upright mounts get extra care. Liquid metal is runny, far thinner than paste. In a vertical GPU or a tilted laptop, extra insulation and a foam dam around the die are worth adding.
If any of those five is a problem, use paste or PTM7950. For more on this setup, see thermal paste for delidded CPUs. Compare it head to head in Arctic MX-6 vs Thermal Grizzly Conductonaut.
Which one should you use?
- New desktop build, stock or mild overclock: paste. Anything decent will do.
- High-end desktop CPU, heavy overclock: a premium paste. Liquid metal under a lid gains only a degree or two, not worth the risk for most people.
- Delidded CPU or direct-die cooling: liquid metal, if every item on the checklist above is covered.
- Repasting a GPU: paste or PTM7950 on the core, and new pads of the correct thickness on memory and VRMs.
- Laptop: PTM7950 or a thick, pump-out resistant paste. See the best thermal paste for laptops.
- PS5, PS4 or Xbox: see the console thermal paste guide. The PS5 already uses liquid metal from the factory, so don't open it just to change that.
- A PC you take apart often: a graphite sheet.
What are the most common mistakes?
- Buying on the W/mK number alone. Consistency, how well it resists pump-out, and applying it correctly matter more.
- Leaving the plastic film on the cooler base. It happens more than anyone admits, and temperatures shoot up straight away.
- Wrong pad thickness on a GPU. This is the most common cause of a card running hotter after a repad.
- Liquid metal on aluminum. The damage is permanent.
- Not cleaning off old paste properly. See how to remove old thermal paste safely.
Browse every paste, pad, phase-change pad, sheet and liquid metal side by side in our thermal paste comparison. Spec terms are explained in the thermal paste glossary.
Worried about a bit of squeeze-out? 133 of the 149 compounds we list are electrically insulating, and the 11 that are not are all liquid metal or graphene. The numbers are in is thermal paste electrically conductive.