Thermally conductive rubber

The first time I saw thermally conductive rubber was many years ago in CD-ROM drives, where it was used to transfer heat from the motor drivers to the drive casing.
At the time, I didn't really appreciate how convenient it was. But much later I realized that it could come in very handy, so out of curiosity I ordered a couple of pieces in different thicknesses to try out.
If you're interested, read on.

Thermally conductive rubber has a simple purpose: to transfer heat from a component that gets hot to a heatsink, enclosure, and so on.
Thermal paste does this very well, of course, but only as long as the gap between the component and the heat spreader isn't too large.
That's where this special thermal conductor comes in handy, since the gap can sometimes be 1, 2, or even more millimeters.

To try it out, I ordered two 100x100 mm pieces, one 1.5 mm thick and the other 2 mm thick. The price in the listing title is for the first one; the second costs a little more.
The rubber also comes in two colors, blue and gray, though I haven't figured out what the difference is. Maybe someone knows.
It arrived in a regular bag, as two little squares.
Both sides are covered with protective film for shipping: thin on one side and thick on the other.


One of the pieces had a small crack. I don't know how it happened, but it was a bit disappointing.


The rubber was cut pretty crookedly, but overall it turns out to be even larger than the promised 100x100 mm.


It's 100 mm on one pair of sides and 105 mm on the other, so they didn't shortchange me here :)
The thickness matches the stated 1.5 and 2 mm exactly. Measuring it isn't easy, since the rubber is quite soft and gets thinner when pressed.


Speaking of weight, when I took the pieces out of the bag, I was a little surprised by how heavy they were. I weighed them out of curiosity.
The thin one weighs 37 g, and the thick one 50 g. That seemed like quite a lot for such small pieces.


There's not much else to describe, so I went on to see if I could measure how it performs compared with other thermal interface materials.

A photo of the testing process. It looks a little scary. Yes, I wrote everything down on scraps of paper, then transferred it to Excel. And yes, I know my handwriting looks like a chicken’s left foot—sorry. I type faster on a keyboard, and the letters and numbers come out much neater, but that wasn’t as convenient at the time.
The whole testing process took about 8 hours (the far-right column on the notes is the time). It took up a good chunk of my desk, made a mess, and heated up an already not-so-cool room. I didn’t want to turn on the air conditioner because I was afraid it might affect the measurements.


And here’s the final result.
The table shows the temperature difference between the resistor and the reference point on the heatsink. That’s why I took these measurements: the absolute temperature by itself doesn’t tell us anything useful.
All measurements were averaged. For example, I took two measurements with the gray pad, and the table shows the average difference between them.
I think I got everything right, but let me know if I mixed anything up and I’ll fix it.
I actually thought mica would perform worse than the thin pad from the power supply.


I’m not going to list pros and cons; I’ll just share what I think.
Thermal pads definitely have their uses, but you need to use them in a way that maximizes the thermal contact area. I also don’t recommend using them at high power—or, more precisely, at high power per square centimeter. They work well for transferring a small amount of heat to an enclosure cover, for example. One particular advantage is that they can transfer heat even from a circuit board, despite small SMD components sticking up from it (they’ll simply press into the pad).
I wouldn’t say you can’t get by without one—I managed for many years—but sometimes it can make life noticeably easier for both electronic components and the designer, so it’s worth keeping some on hand. I’d recommend having 1 mm and 1.5 mm pads in reserve rather than 1.5 mm and 2 mm ones, since you can easily stack two 1 mm pads to make 2 mm.
Apparently, 0.5 mm pads are available too, and I’ve definitely seen pads as thick as 6 mm.
I’ve seen gray, blue, and pink ones. I couldn’t figure out what the difference is, but the store has listings in both colors for each size. I can sort of understand pink and blue, but why gray… :))))

The thermal pads for testing and review were provided by the tmart store.

I hope my review was useful, even if it was very short. Feel free to ask questions; I’ll be happy to answer.

The product was provided by the store for review.