K5 Pro, or what to do when you don't have any thermal paste on hand

Some time ago, one of my readers contacted me privately and asked me to do a small comparative test of several thermal interface materials.
I was interested in doing this too, especially since I had already done a similar test, so I decided to help out.
As it happened, though, the idea grew into a somewhat larger test, and a slightly unusual one at that.

The original task was to compare two thermal interface materials: K5-pro, bought on eBay, and a thermal pad. But the reader also sent me some thermal tape, just for the sake of experimentation.
The package contained three types of thermal interface material in all.
K5pro — link
Arctic thermal pad, 1 mm thick, bought from the manufacturer's store — link.
Alphacool thermal tape, 0.5 mm thick — link

I also tested several other options along the way, but I'll tell you about those as I go.


The manufacturer positions this paste as a replacement for thermal pads—that is, for situations where there is a significant gap between the heatsink and the heat-generating component.
The test was essentially meant to find out which is better: K5pro or the Arctic pad.

The paste comes in a tube with a lipstick-style dispensing mechanism.
It's quite thick, light gray, and the tube is marked Computer Systems. Made in Greece; net weight: 10 grams.


I put together the same test rig as in my previous review. More precisely, not just the same kind of rig, but the very same one. Since then, I'd put everything I used for the previous test away in a drawer and hadn't touched it, so this test is fully identical to the first one.


For the first test, though, I chose not to compare thermal paste with a thermal pad, but to test only the paste, using two different thicknesses.
Since I'm ultimately measuring the temperature difference, the order and what exactly I test don't matter.


As I understand the manufacturer's instructions, you should dispense roughly twice as much paste as you need. The result should look something like this.


The manufacturer also has a video showing how it's done.


Since my “test rig” doesn't let me set a specific gap between the heater and the heatsink, I had to create the required clearance myself.
To do that, I took some edge banding about 0.5 mm thick and cut six small strips. I arranged them in a single layer for one setup and in two layers for the other.
Then I filled the remaining space with paste and installed the heaters.


As intended, the excess paste was squeezed out. The test isn't entirely accurate, since the spacers covered about 10–15% of the heater's surface area, reducing its effectiveness accordingly. This needs to be taken into account in the final measurement.


I entered the interim test results in a spreadsheet. As last time, the test ran for one hour, with measurements taken every 10 minutes.


Next came a test of 0.5 mm-thick Alphacool thermal tape and 1 mm-thick Arctic thermal pad.
Arctic pads are considered very good quality, so I was especially curious to see what this one could do.


I think the result is very good, but I wasn't too impressed with the tape.


After that, I ran a few more tests just out of curiosity.
First, I compared KPT-19, which is marketed as non-drying, with KPT-8 from a new batch. Last time, I tested some rather old KPT-8.


The results are almost identical, but KPT-8 is still slightly better.


For this test, I used the cheapest Chinese thermal paste that comes bundled with coolers. I had it in one of my reviews. I also used some basic double-sided tape from the nearest supermarket.
I'd been meaning to try double-sided tape for a long time, but never got around to it. Is it really that bad, or is special thermal tape actually better?


The result really surprised me. I understand that this tape is about half as thick as Alphacool's, but it costs a lot less, and performs just as well.


Now let's get to what I mentioned in the title.
In this test, I tried applying KPT-8 in a very thin layer. People often tell me in the comments that I'm “eating my sandwich the wrong way,” so I decided to put that to the test.
But I also tested another material that can be used as a thermal interface.
I was talking to a friend once, and he said he'd replaced the CPU fan and wiped off the thermal paste, then realized he had nothing to replace it with. He had to rush out and buy some, and it was already a weekend evening.
I told him, “But your garage is right nearby. You could've gone and got some solidol and smeared it on. It's more than good enough as a temporary fix.” He was surprised, just as I was, because I thought this was common knowledge.
But in practice, it turns out that not everyone knows that when you need something “right here, right now,” rather than “tomorrow, somewhere else,” you can use plain solidol.
So I decided to run a comparison test to see how solidol performs in this application.
The solidol was old, probably 15 or even 20 years old. I applied it just like ordinary thermal paste.


And the result was only slightly worse than KPT-8 :)


Now we can sum things up. Some of the results are interesting, while others are disappointing.
K5 Pro thermal paste didn't live up to expectations; the Arctic pad performed better.
It also turns out that ordinary supermarket tape conducts heat just as well as the special stuff. The only difference is that supermarket tape may not last as long.
KPT-19 performed slightly worse than KPT-8.
Applying KPT-8 in a thin layer improves the result by just half a degree.
Solidol can certainly replace thermal paste in a pinch.

I've put the test results in a table. It shows the temperature difference between the heater and the heatsink, so a higher number is worse.
The K5 thermal paste result was adjusted by 15% to compensate for the reduced heat-transfer area.


Along the way, I'll include a table from my previous review.


There won't be a list of pros and cons today; everything is covered in the review. All I'll say is thanks to the review's “sponsor,” and happy birthday to them.

If you have any test suggestions, let me know. I'll check them out when I can.

At the many readers' request, I ran four more tests.