What Is Thermal Paste Viscosity?
If you’ve worked with thermal pastes before, you might have noticed some of them are denser, while others are more like a liquid. Both of these have their equal share of pros and cons. For instance, a thick or dense thermal paste could be hard to spread on the CPU, while a thin paste could be harder to control and dry out faster.
Why is that? What makes a thermal paste dense and the other one very thin? Well, the term you’re looking for is “viscosity”.
What is thermal paste viscosity? Is it important?
In simple words, the viscosity of any paste/liquid is its density. The denser a liquid, the higher the viscosity.
A low-viscosity thermal paste behaves more like a liquid, i.e., it might flow easily, and spread easily, but it’s also harder to control and dries out faster.
A high-viscosity thermal paste, on the other hand, behaves more like a solid. It doesn’t flow that easily and could be harder to spread using a spreader or spatula. But — it sits better on the CPU once you have applied it correctly.
Simply put, you don’t want a paste that’s too thin or too thick. So, yes, keeping the viscosity in consideration is important.
How viscous should thermal paste be?
The scientific unit for viscosity is Newton-second per meter square, which is usually expressed in Pascal-second (Pa·s) or milliPascal-second (mPa·s). p.s. 1 Pa·s = 1,000 mPa·s
On the market, you can find thermal pastes ranging from 300 units to 1500 units. As said earlier, a thermal paste with less viscosity will be too thin, and won’t stay on your CPU firmly. On the other hand, a high-viscosity thermal paste would be too hard to spread and apply.
So, what do you select? You need a paste that isn’t too viscous that it’s hard to spread, but isn’t too thin either so that it dries out faster.
Is high viscous or low viscous thermal paste good?
If you’re considering which one is a better buy, a high-viscosity paste or a low-viscosity one, let us help you out. In most cases, you want to avoid both of them.
A high viscosity paste is very difficult to apply and spread on your CPU’s surface. If you’re using the buttered toast method, your spatula will find the paste too dense and hard to move.
If you use another method that relies a lot on the heat sink’s weight, say the one-dot method, a dense thermal paste won’t work well in this case, too. That’s because the pressure of the heat sink put on top won’t be able to spread the paste enough to cover the entire surface of the CPU. (Learn more about What Is the Best Thermal Paste Pattern? Actual Performance Comparison )
While a low-viscosity thermal paste is comparatively easier to apply because of its thin formation, it doesn’t work well for long. Manufacturers add an organic solvent into their thermal pastes to make them thinner. When you apply a low-viscosity thermal paste and start using your computer, the organic solvent starts evaporating with heat.
When that happens, the paste gradually loses its liquid properties and dries out. When it’s partially or fully dried out, it cannot fill in all the air gaps between the CPU and the heatsink anymore, hence the thermal performance of your computer suffers a lot.
So, in reality, neither a too-thin nor a too-thick thermal paste is an ideal solution.
What you need is a paste that’s easy to spread, but doesn’t utilize any organic solvent in its formation, so that it can last long.
Fortunately, we have built a thermal paste with those exact properties, and we call it Kooling Monster KOLD-01.
KOLD-01 has no organic solvent, which means it doesn’t dry out no matter how hot your computer components get with usage. Furthermore, due to the unique rheological structure, it behaves like an easy-to-move paste when you apply pressure on it. When you release the pressure, it sits firmly in its place and fills in all the air gaps ideally.
What happens if my thermal paste is too viscous?
If you’ve made the mistake of buying a thermal paste that’s too viscous, and are now having problems applying it, let us help you out.
Some believe adding organic oil to the paste will do the job by making it less viscous. But it doesn’t work that way. It’s not recommended to add any third-party solutions to your thermal paste. It should be used as it comes out of the box. If you do add something to it, the thermal performance might suffer drastically.
What we recommend is that you get rid of the paste altogether and start over. Get a thermal paste that’s less viscous. But again, you might end up with a thermal paste that’s too thin, thanks to the added organic solvent. So, the best course of action is to get a thermal paste that offers the best of both worlds.
The bottom line
Thermal paste viscosity is a subject many newcomers are confused about.
What is viscosity? How viscosity should a thermal paste be? Should I pick a paste with low viscosity or high viscosity? These questions often haunt new computer nerds trying to apply thermal paste on their own.
Ideally, you must look for a paste that’s neither too viscous nor too thin. Plus, it shouldn’t have any added organic solvent to decrease its viscosity.