by Sergey Lepilov
03/03/2011 | 12:39 PM
The effect of thermal interface should not be underestimated in the world of CPU and GPU coolers where much effort is spent to lower the temperature of electronic chips by even one or two degrees. Coolers have got so sophisticated nowadays that we cannot expect a dramatic breakthrough in their performance. A new model can only be expected to win 1, 2 or, rarely, 3°C against its predecessor, but just as likely there can be no improvements at all. This is why we must note disregard the efficiency of thermal grease which can often provide more benefits than a replacement of the cooler proper.
If you are not in the know, thermal interface is a material that ensures effective heat transfer between a hot component and its heatsink. When it comes to computers, the component is a CPU or a GPU. The more effective that material is, the lower the temperature of the component and the higher its overclocking potential. Sounds simple, but things can get more complicated in practice.
So, I have collected a number of thermal interface materials (some of them just didn't fit into the photo) to carry out a comparative test:
This test is split up into two parts. Part 1 that you are reading now concerns with 26 thermal interfaces that sell as individual products. Part 2, to be published later on, will cover thermal interfaces included with coolers as a free accessory.
Let's now check out each interface and their properties.
The table below sums up all the technical specifications of the tested thermal interfaces as stated by their manufacturers. Unfortunately, in many cases there are only two-three key things mentioned. Nevertheless, the table below contains all the information we managed to find on each of the tested products:
First go two thermal greases from the Swiss firm Arctic Cooling. These are ARCTIC MX-2 and ARCTIC MX-3. Unfortunately, I couldn't get the new ARCTIC MX-4, but you will see its clone in this review anyway.
The two products are shipped in different ways. The ARCTIC MX-2 comes in a 30-gram syringe ($26.5) packed into a paper box with an open top. The ARCTIC MX-3 comes in a 4-gram syringe ($12.3) packed into a plastic blister wrap.
The ARCTIC MX-2 is also shipped in packs of 4 ($7.9) and 8 grams ($11.8) whereas there are no other capacities available for the MX-3. By the way, the ARCTIC MX-3 is not officially produced by Arctic Cooling anymore but can still be found in shops. Interestingly, both thermal greases are produced in the United States but packaged in Taiwan.
The name of the product and a manufacturer logo are printed on each syringe.
Each of these thermal greases is a silicone compound with carbon particles. The MX-3 features an improved formula and is targeted at enthusiasts as it provides an advantage of 2.5°C over the MX-2. Both are dielectrics. They do not leak or dry out. Arctic Cooling claims they can be reused and keep their properties for as long as eight years! It's hard to say if this is true or not, because I personally didn’t use the MX-2 for more than a year, yet I must admit that it didn’t dry out over that time.
The MX-2 and MX3 are both a similar gray in color but differ in consistency.
While the MX-2 is viscous, the MX-3 is somewhat drier and kind of hard. It is rather difficult to apply the latter on a component you want to cool. You have to stretch that thermal grease over the surface, yet it is next to impossible to get a very thin layer of it. By the way, this property of the MX-3 was the reason for the manufacturer to discontinue its production. The new MX-4 combines the plasticity of the MX-2 with the high efficiency of the MX-3. The thermal conductivity of the ARCTIC MX-2 is not specified whereas the MX-3’s is specified to be 8.2 W/(K·m), which is among the highest values in this test session.
That's how these thermal interfaces looked on a GPU and a cooler base after my tests.
|ARCTIC MX-2||ARCTIC MX-3|
I had no problems removing them both from the surfaces afterwards.
The Arctic Silver Matrix is a rather new product that sells for about $6 for a 2.5-gram syringe without additional packaging.
Despite the small capacity of the syringe, the manufacturer claims it will be enough for 20 uses. The official website doesn't tell anything about the characteristics of this thermal grease, so we can only judge its efficiency by the test results. Its operating temperature is specified to be in a range of -50 to +135°C. The Silver Matrix takes about 300 hours to break in.
This thermal grease is gray and viscous.
It was easy to apply to and remove from the surfaces, though. I didn’t find it difficult to get a thin and uniform layer of it.
By the way, the Arctic Silver Matrix is an inexpensive version of the Arctic Silver 5 we will take a look at right now.
The Arctic Silver 5 is a time-tested overclocker-friendly thermal interface. It is widely regarded as an etalon among thermal greases and new products are often compared to it. I've got it in a new large 12-gram syringe for $23.
It is available in a smaller and cheaper portion: 3.5 grams for $8. The Arctic Silver 5 features a very high thermal conductivity of 8.7 W/(K·m), which is the second highest value in this review (excepting the liquid metal). It is made of zinc oxide, aluminum oxide and boron nitride particles. Its color is silvery gray and it is viscous but not hard. A strong adhesion is a special feature of the Arctic Silver 5. It does not contain silicone, a unique mix of synthetic oils serving as the binding agent. The Arctic Silver 5 does not conduct electricity, does not leak and does not dry out. It achieves its peak performance in 50 to 200 hours and keeps it for a long period of time (the exact period is not specified, though).
This thermal grease is easy to apply and smudge on a component surface to get a thin and uniform layer of it.
There are also no problems cleaning the component from this grease afterwards. By the way, the Arctic Silver website offers detailed instructions on applying the thermal grease on most CPU types.
The Cool Age CA-CT3 Nano comes in a small 2-gram syringe with no packaging.
Manufactured from nano-particles, the Cool Age CA-CT3 is specified to have a thermal conductivity of 5 W/(K·m) and a thermal resistance of less than 1.194°C-cm2/W. No other parameters are declared.
This thermal grease is thick but soft. It is very sticky and its color is light gray.
The Cool Age CA-CT3 Nano is a dielectric. It does not leak and does not dry out for a long period of time. Thanks to its plasticity and, perhaps, to those nano-particles, I easily got it spread out in a very thin and uniform layer. Its imprint on the GPU and heatsink surfaces was just exemplary:
This thermal grease was also easy to remove.
The Coolink Chillaramic is shipped in a small cardboard box with a cutout in its front and information about the product on the back.
The syringe contains 10 grams of thermal grease which, according to Coolink, should suffice for 30 uses on a CPU.
This thermal grease resembles thick sour cream and is the same white color.
The Coolink Chillaramic claims to combine high efficiency and ease of use thanks to ceramic nano-particles. However, the manufacturer does not declare the thermal conductivity of this thermal grease, mentioning only the relative density with respect to water (3.2 g/cm3) and the operating temperature range (from -35 to +85°C).
This thermal grease does not conduct electricity and does not dry out but I have some apprehensions about its not leaking. Compared to the other products, the Chillaramic is perhaps the most fluid of all. On the other hand, it is very easy to apply:
This thermal grease is also easy to remove. The Coolink Chillaramic costs about $9.
Besides pretty good coolers and fans, Deepcool offers three thermal interface materials. I will discuss the best of them here. It is called Z9.
The syringe with this thermal grease is shipped in a transparent blister pack with a paper insert.
The product is manufactured in China and sells for $12. The syringe contains 7 grams of thermal grease.
The Deepcool Z9 is specified to have a thermal conductivity of 4 W/(K·m). Its thermal resistance is expected to be no higher than 0.374°C-cm2/W. The operating temperature range spans from -40 to +200°C.
This thermal grease is rather viscous, but not too dry. It is gray in color.
The Z9 is easy to apply and distribute in a thin and uniform layer on a component surface.
I also had no problems cleaning the processor and cooler from the Deepcool Z9 after my tests.
Evercool’s marketing folks have come up with an original name for their thermal grease, perhaps associating it with a cruise missile that always hits the target. I guess they should instead have consulted with the engineers about what this gray stuff in the syringe does in order to offer a more relevant name. If they wanted to pursue the military theme, a name like Thermal Mine might be appropriate, I think. :)
The Cruise Missile comes in a large and originally decorated box.
Designed in the military style, the box protects the product against any hazards during transportation and is also informative.
The small syringe with a red cap contains only 3 grams of thermal grease.
The Cruise Missile is specified to have a thermal conductivity of 2.89 W/(K·m) and a thermal resistance of 0.032°C-cm2/W. Running a little ahead, I can tell you that two more products in this test session have the same specs but perform differently.
This thermal grease is gray, soft and viscous.
It is easy to apply and remove from any surface.
The Evercool Cruise Missile costs about $12.
Gelid Solutions Ltd. provided three products for today’s tests: GC-1, GC-2 and the new GC-Extreme. They all have similar packaging:
As the GC-1 is already out of production, I will focus on the two new products even though I’ll test all three. The syringes with the GC-2 and GC-Extreme differ in capacity: 7 and 3.5 grams, respectively.
A small plastic spatula is included with each product to make it easier to apply the thermal grease. The thermal conductivity of the GC-2 is not specified whereas the GC-Extreme is declared to have a high thermal conductivity of 8.5 W/(K·m). The operating temperature range is not specified for these products. I can only add that the Gelid thermal greases do not conduct electricity, do not leak and do not dry out for a long period of time. Gelid does not tell anything about what components are used in these thermal interfaces.
The Gelid greases are all light gray in color.
They differ in consistency. The GC-1 is the most fluid among the three and the GC-2 is the thickest. The GC-Extreme is in between the previous two in terms of consistency, being very soft and rather sticky. The difference between these thermal interfaces can be easily spotted by their imprints on the GPU and cooler's base:
|Gelid GC-1||Gelid GC-2||Gelid GC-Extreme|
Despite the different consistency, each of the Gelid thermal greases was equally easy to apply and remove from the surfaces. The GC-2 costs about $7 and the GC-Extreme costs $10 although the latter comes in a syringe only half the capacity of the GC-2 one.
GlacialStars is a daughter brand of Glacial Tech Inc. Its thermal grease is called IceTherm II. It is included with the company's new coolers and is also available as an individual product. I received it without any packaging in a small syringe, though.
There is only 1.5 grams of this China-made grease in it. The syringe costs $5.
The GlacialStars IceTherm II is specified to have a thermal conductivity of 8.1 W/(K·m). It retains its properties within a temperature range of -40 to +100°C.
This light-gray grease is of medium thickness.
I had no problems applying and scraping the IceTherm II off the processor and cooler.
Perhaps the most exciting product in this review, the Indigo Xtreme comes in a plastic blister wrap with a sticker on the face side.
The kit contains a user guide, two soaked napkins, two dry napkins, rubber gloves, and two samples of the thermal interface.
The Indigo Xtreme is an overclocker-targeted thermal interface that is something in between ordinary thermal grease and liquid metal. Its specified thermal conductivity is over 20 W/(K·m) and its thermal resistance is the lowest among all thermal greases available on the market (although the exact number is not declared). Enerdyne Solutions, the manufacturer of the Indigo Xtreme, calls it Engineered Thermal Interface and claims that its advantage over conventional products increases at higher loads. For example, at a load of 130 watts the Indigo Xtreme is going to outperform the Arctic Silver 5 by about 4°C and the gap will grow larger at even higher loads.
The Indigo Xtreme is not an all-purpose interface due to the way it is applied on the processor. There is a particular version of it for each CPU type. Here is the LGA 1366 version of the Indigo Xtreme, for example:
The kit includes two samples of the Indigo Xtreme for two uses. The thermal interface is sealed within two films. There are stickers on top of the films telling you where the top and bottom of the interface are.
The orientation is important because the Indigo Xtreme will not work if applied incorrectly. Besides, it will not work with direct-touch coolers that have aluminum inserts and gaps between heat pipes. It is also incompatible with coolers (or water-blocks) that have a round base.
The procedure for applying and removing this thermal interface is detailed in the included manual as well as at the official website. There is an unofficial video guide, too. In fact, the procedure is even simpler than with conventional thermal grease. First you should degrease both surfaces with the wet napkins (they have a pungent and obnoxious odor, by the way) included into the kit. Then you peel off the bottom film and glue the Indigo onto your CPU. After that you peel off the top film and put down and fasten your cooler. That’s how the Indigo Xtreme looked when installed on an LGA1366 processor, before and after my tests:
That is, the thermal interface is supposed to spread out on the CPU heat-spreader under the pressure of the cooler’s base. This happens when the CPU is hot because the Indigo Xtreme changes its structure at temperatures within 60 to 100°C. My six-core Intel Core i7 980X processor working at its default frequency had a temperature of 77°C when loading the BIOS. When the OS booted up and I launched a brief test from the AIDA suite, the CPU temperature rose above 100°C.
I then referred to the user guide and read that the thermal interface had to melt and spread out on the CPU heat-spreader during 2 to 3 minutes of working at a temperature of 90°C. So I ran the test a few times more but to no effect. The Indigo Xtreme didn’t spread out on the surface more than in the photo above. The mainboard was oriented horizontally, just as required according to the user guide, and I turned the computer on and off twice just as necessary, but the result was unsatisfactory.
I supposed that the problem might be in the Coolink Corator DS cooler which had no trace of the thermal interface when I took it off:
So, I applied a new sample of the Indigo Xtreme on the processor once again:
And then I used a Zalman CNPS10X Performa cooler. I kept the CPU under load constantly for 10 minutes and then in cycles during 15 minutes more, keeping its temperature at 90°C, in order to finally melt the Indigo Xtreme. But despite all my efforts, I could not make that thermal interface work.
Perhaps my sample of the Indigo Xtreme had sat in the lab for too long (over a year) before I tested it or there may be some other reason, but the fact is I could not make it work properly. So, this thermal interface will not take part in my tests, unfortunately.
In fact, I don’t really understand how this fluid thermal interface can get under the cooler’s base which is tightly fastened to the CPU heat-spreader with screws. Perhaps the screws should be released while melting it? There must be some reason for that problem because the Indigo Xtreme is considered one of the best thermal interfaces among computer enthusiasts and is reported to deliver high efficiency as well as stable and repeatable performance.
I can only add that the Indigo Xtreme costs about $20.
Next go two products from Nanoxia: Heat Buster Zinc Thermal Grease and Nano TF-1000 Fluid Metal Thermal Grease. Both products are shipped in antistatic packs with small stickers.
Each pack contains a syringe with thermal grease.
Although the company’s official website is down for some reason and there are no specs on the packs, I could find out that the specified thermal conductivity of the Heat Buster is 10.4 W/(K·m), which is the highest value among all the products in this review. The Nano TF-1000 is nothing else but liquid metal.
The gray-colored, thick and viscous Heat Buster can be easily applied and removed, just like the majority of other thermal interfaces.
As for the liquid metal, it may provoke some problems, especially for inexperienced users. One thing you should know is that you must not leave this thermal interface on the processor like this:
The drops of liquid metal will surely roll to the edges of the GPU die and close some contacts there when you install your cooler. One way to apply this thermal interface is to soak some pileless fabric in it and smudge it all over the surface in a thin layer. Unfortunately, I didn't keep that photo through my own fault and did not want to repeat the procedure to make a new photo because it was very hard to clean the surfaces from the liquid metal, but the result will look something like that (click the link to see the photo).
Both thermal interfaces from Nanoxia are manufactured in Germany. The Heat Buster costs about $7 for a 2-gram syringe. The NanoTF-1000 costs $10 for 0.5 grams.
The Japanese firm Scythe Co. is represented with its Thermal Elixer in this review. The product comes sealed into a small paper and plastic package.
You will only find a 3.5-gram syringe with thermal grease inside. It is manufactured in Taiwan.
The Scythe Thermal Elixer has the same specs as the above-discussed Evercool Cruise Missile: a thermal conductivity of 2.89 W/(K·m) and a thermal resistance of 0.032°C-cm2/W. Its color is light gray.
This thermal grease is viscous and elastic. It can be easily spread out in a thin and uniform layer.
The Scythe Thermal Elixer costs about $10.
Now it’s time to take a look at a product from Thermalright Inc., a leading manufacturer of air-based cooling solutions. The thermal grease is called Chill Factor III and is a third such product from Thermalright. To be exact, the first two were not individual products but were included with the company’s coolers. I will test them in the second part of this review.
So, the small tube with thermal grease and a card for spreading it on a CPU are packed into a transparent plastic blister wrap with a paper insert:
There is only 4 grams of thermal grease inside. It is manufactured in Taiwan and costs about $10 in retail shops.
I do not know much about the official specs of the Chill Factor III. Its thermal conductivity is declared to be no lower than 3.5 W/(K·m) and its thermal resistance is 0.032°C-cm2/W. Thermalright claims the Chill Factor III to “bring a new era of thermal interface materials”. This grease does not conduct electricity. It doesn't leak, dry out or burn. Its color is gray.
Being dense in consistency, the Chill Factor II features a unique composition that makes it very plastic and viscous. It is no harder to apply it on a CPU than most other thermal greases. It spreads out in a thin and uniform layer.
Thermaltake is represented by two products: TG-1 (CL-O0027) and TG-2 (CL-O0028). Both are packed into transparent blister wraps.
The first product is targeted at enthusiasts who are ready to shell out $13 for 4 grams of thermal interface. The second one is an entry-level alternative and comes in a same-capacity tube for only half the money. Both are manufactured in Taiwan.
The Thermaltake TG-1 and TG-2 are specified to have a thermal conductivity of 3 and 1.5 W/(K·m), respectively. The TG-1 can work within a temperature range of -40 to +150°C; the operating temperature range of the TG-2 is not specified. Both are dielectrics and are expected to retain their properties for two years of use.
They differ in color, the TG-1 being somewhat darker.
The lighter TG-2 is also more fluid, although both are rather easy to apply and remove.
|Thermaltake TG-1||Thermaltake TG-2|
The Titan Royal Grease (TTG-G40030) comes in a lightproof pack with a small sticker.
Inside you will find a slim tube with 3 grams of gray-colored thermal grease.
The Titan Royal Grease has the same specifications as the Evercool Cruise Missile and Scythe Thermal Elixer. I wouldn’t be surprised to learn that these are actually one and the same thermal grease selling under different brands, as is often the case with CPU coolers. The Royal Grease specs also mention the operating temperature range: -50 to +240°C. This grease retains its properties for 2 years.
Here are the imprints left by the Titan Royal Grease on the processor and cooler:
You can buy it for about $7.
The Tuniq TX-3 has been manufactured for over a year and a half already and is considered one of the best thermal interfaces for overclocking. It comes in a transparent blister wrap with a paper insert. You can find the product specs on the back of the packaging:
The small tube, manufactured in China, contains only 3 grams of thermal grease which will cost you $5.
The TX-3 is gray and dense. Its thermal conductivity is specified to be 6.2 W/(K·m). Its operating temperature range goes from -45 to +200°C.
The Tuniq TX-3 is similar to the ARCTIC MX-3 in consistency and density, so it is not very easy to spread it out thinly. Anyway, if you apply enough force, you should get a uniform layer:
The newer Tuniq TX-4 is the next step in the development of this thermal interface. It is rumored to be the ARCTIC MX-4 selling under the Tuniq brand, by the way. I don't know if this is true, but the Tuniq TX-4 comes in original packaging which is compact, reliable and rather informative.
A plastic card for spreading the thermal grease on the CPU is included with the 3-gram tube.
Take note that the sizes of the heat-spreaders of modern CPUs are marked out on that card.
The Tuniq TX-4 differs from the TX-3 in having a somewhat higher thermal conductivity (6.53 W/(K·m)), a different operating temperature range (-45 to +160°C), and different consistency. It has become more fluid and thus easier to apply on a CPU surface. The color hasn’t changed:
Tuniq says that the new TX-4 should be 1°C more effective than the TX-3.
Here is the imprint left by the Tuniq TX-4 on the graphics processor and cooler:
The amount of thermal grease being the same, the Tuniq TX-4 is twice as expensive as the Tuniq TX-3 and costs $10.
Like the Tuniq and many other thermal interfaces, the Xigmatek PTI-G3606 is packed into a plastic blister wrap.
The 3-gram tube is manufactured in China and costs about $6. A small spatula is included with it for spreading the thermal grease on a processor surface.
The Xigmatek PTI-G3606 is declared to have a thermal conductivity of 5 W/(K·m). Its operating temperature range is -20 to +180°C.
This thermal grease is gray.
It is also rather fluid, so it is very easy to apply and remove it from any surface. Here are the photos of its imprints:
Xilence is represented in this review by two products: SilverTim (ZUB-XPTP) and X5 (ZUB-XPTP.X5). Both are manufactured in China and come in transparent plastic packs:
The product specs and even compositions are listed on the backs of the paper inserts. The tubes themselves are not very informative.
Compared to the other products in this review, the thermal interfaces from Xilence are very open about their characteristics. Their thermal conductivity is declared to be rather low at 1.45 W/(K·m) for the X5 and 1.134 W/(K·m) for the SilverTim. The thermal resistance is 0.023°C-cm2/W for the X5 and 1.333°C-cm2/W for the SilverTim. The operating temperature range differs, too: from -50 to +300°C for the X5 and from -30 to +240°C for the SilverTim. Despite the differences in their specs, the two thermal greases are priced at a similar level, below $4.
Their color is similar, too, but the X5 is denser than the almost liquid SilverTim.
You can see that in the photos:
|Xilence SilverTim (ZUB-XPTP)||Xilence X5 (ZUB-XPTP.X5)|
Each of these interfaces is easy to apply and remove without any trace.
The Zalman ZM-STG2 accompanies Zalman’s new coolers and is also available as a standalone product for $6. One tube contains 3.5 grams of this thermal grease.
The Zalman ZM-STG2 is declared to have a thermal conductivity of 4.1 W/(K·m) and a thermal resistance of 0.08°C-cm2/W. Its operating temperature range is -45 to +150°C.
This thermal grease is dense and viscous.
It is easy to apply in a thin and uniform layer and later remove from a processor.
That’s the last of the products to be tested. Let’s move on to the tests now.
It is far more difficult to test thermal interfaces than, for example, coolers because the difference between them is much smaller. You have to catch a difference of 1°C or less, which is a nontrivial task if you don't have a thermal chamber. For thermal interfaces to differ more notably, it is necessary to put them under such conditions that they are the weakest link in the heat transfer chain between the processor die and the ambient air. To do this, a high-wattage heater and a very efficient cooler are needed. There is no problem to find the former. As for a cooler, a liquid cooling system would be a perfect choice, but it would be much harder to deal with in terms of replacing the thermal greases. Moreover, this test wouldn’t have much practical value because liquid cooling systems are far less popular than air-based coolers.
So, carrying out such tests and ensuring repeatable results is not a trivial task.
For our test session we assembled the following test platform:
That’s a photo of my system during the tests (except for the Indigo Xtreme which was tested with the mainboard oriented horizontally):
The ambient temperature was monitored with an electronic thermometer and varied from 23.9 to 24.5°C during the tests. The test results were normalized to 24°C by adding or subtracting the deflection of the ambient temperature from that value to or from the result of each thermal interface. By the way, if I was standing next to the system case during the test, the air temperature would grow up by 0.2-0.3°C.
I tested the thermal greases using the GPU of an AMD Radeon HD 6950 graphics card transformed into a Radeon HD 6970 by rewriting its BIOS.
The Cayman processor is the largest of open-die GPUs and is also among the hottest. I don't think there is a graphics card better suitable for such tests. I also used one of the most efficient coolers available: an Arctic Cooling Accelero XTREME 5870.
The rotation speed of the cooler’s three fans was fixed at the maximum 1920 RPM.
The cooler’s base is ideally flat and smooth, even though it seems rather rough.
Each thermal grease was applied in a thin and uniform layer on the GPU die. Each was applied twice, with both surfaces being cleaned and degreased with alcohol between the tests. When applied, the thermal grease was left working for 1 hour to “break in” before the test proper. I ran Unigine Heaven 2.1 at 2560x1600 with 16x anisotropic filtering for that. After this warming up and when the GPU temperature had stabilized (this would take about 10 to 15 minutes), I would begin the test proper.
During the test the graphics card was running FurMark 1.8.2 launched from a renamed EXE-file at 2560x1600 with 16x anisotropic filtering enabled in the Catalyst driver. I used two monitoring tools: GPU-Z version 0.5.0 and MSI Afterburner 2.1.0 beta 5.
There were at least two such test cycles with a 20-minute pause for cooling down and stabilizing the temperature. I did this with each thermal grease for a total of over 50 test cycles. I didn’t overclock the computer when testing the thermal interfaces with the GPU.
I also tested some of them with my CPU. It would have taken extremely long to test every product on the CPU, so I took only four of them of that, including the Indigo Xtreme. The other three were the best, medium and worst performers in the GPU tests. Another reason why I didn't test all the products on the CPU is that the heat-spreader of my Intel Core i7 Extreme Edition i7-980X processor is not flat but convex.
I took a Coolink Corator DS cooler with Gapless Direct technology for testing the mentioned thermal greases with my CPU. It is a direct-touch cooler that doesn't have any gaps or aluminum inserts in its base. Theoretically, the thermal interface should have a higher effect on cooling with a direct-contact cooler than with a classic cooler because one heat transfer is eliminated (from the cooler's base to the heat pipes). To make the Corator DS even more effective, I replaced its 120mm fan with two 140mm Thermalright TY-140 fans which were working at their maximum speed of 1310 RPM.
To increase the amount of heat produced by the CPU, I overclocked it to 4.25 GHz, setting its voltage at 1.375 volts in the mainboard's BIOS.
The Turbo Boost technology was disabled whereas Hyper-Threading was turned on. Why did I use Hyper-Threading now but never do so in my CPU cooler tests? It’s because of the program for heating the CPU up. Using Linpack with the LinX frontend does not produce adequate results in tests of thermal interfaces because the Linpack load, although very high, is unstable and not very repeatable. When testing coolers, I can easily re-launch Linpack as soon as I spot it yielding gigaflop calculations greatly different from previous results (and this happens quite frequently I must tell you), but it would be too time-consuming in thermal interface tests.
So, I turned to the latest version of Prime95 x64 for a linear and stable CPU load. I launched it in the maximum-load Blend mode for 30-40 minutes during each test cycle.
The temperature of the CPU cores was monitored with the RealTemp utility. The average temperature across the six cores was then corrected according to the ambient temperature (24°C). Like on the GPU, each thermal grease was tested twice, the best of the two runs being regarded as the end result if the difference between the two runs was not higher than 1°C. If the difference was larger, I applied the thermal grease a third time and reran the warm-up and test cycle.
And the last thing: when applying each thermal grease for the first time, I threw away the first few millimeters of what I squeezed out of its tube to minimize the effect of the product's lifetime on its consistency and properties. Just another measure towards more accurate test results.
Now let’s see how the thermal interfaces perform on the open GPU die:
I had no doubts about the efficiency of the liquid-metal Nanoxia TF-1000 even though its advantage amounts to only 1°C of peak GPU temperature in comparison with the other products. The leader is followed by as many as 12 thermal interfaces from the Thermaltake TG-1 to the Nanoxia Heat Buster which differ by about 3°C in terms of peak GPU temperature. The renowned brands are all in this group. We can only note that the Tuniq TX-4 and ARCTIC MX-3 do not have much advantage over the TX-3 and MX-2, respectively. The Glacial Stars IceTherm II is the cheapest thermal grease in the leading group.
Next goes a group of eight products, differing by less than 1°C amongst themselves and by about 2°C from the leaders. It is rather surprising to see the Arctic Silver 5, which used to be a recognized leader, in this group as it is inferior even to its entry-level cousin Arctic Matrix. Perhaps its low results are due to the lack of time for “breaking in”.
The group of losers includes liquid greases like the Xigmatek PTI-G3606, Deepcool Z9 and Thermaltake TG-2. By the way, Thermaltake's two products take the top and last places in the standings if we don't count in the liquid metal Nanoxia and the Indigo Xtreme. The difference between the same-brand products amounts to 12°C!
Next I checked out the efficiency of three thermal greases with my CPU. First I took the Thermaltake TG-1 as the best performer in the previous test:
The Scythe Thermal Elixer represented a medium-efficiency product.
And the Thermaltake TG-2 had the worst result in the previous test:
So, here is how these three performed with my CPU:
So, the standings have not changed but the gaps between the products have diminished. The leader Thermaltake TG-1 is superior to the Scythe Thermal Elixer not by 3°C as on the graphics processor but by about 2°C only. The worst thermal grease of this test session, Thermaltake TG-2, is now only 5°C worse than the leader although the difference was as large as 12°C on the graphics processor. I guess this must be due to the convex heat-spreader of my six-core CPU. The ideally flat die of the graphics processor and the graphics cooler with a perfectly flat base provided much better test conditions.
I also tested these three thermal greases with a Zalman CNPS10X Performa cooler (with two Thermalright TR-FDB fans at 2040 RPM set for exhaust and intake) and received the same results.
Comparing the thermal interfaces by pure efficiency, the Nanoxia TF-1000 is expectedly the best in today's tests as it is based on liquid metal. However, you must keep it in mind that liquid metal is difficult to apply on and remove from component surfaces and is likely to make your CPU and, especially, graphics card warranty void. Besides, it is not cheap. The new-fangled Indigo Xtreme might be as efficient as the liquid metal and also much easier to use, but I could not make it work in my tests.
Then, the group of high-efficiency thermal interfaces includes as many as 12 products from ten brands: Thermaltake TG-1, Tuniq TX-3 and TX-4, Thermalright Chill Factor III, Gelid GC-Extreme, Cool Age CA-TC3 Nano, Nanoxia Heat Buster, Arctic MX-3 and MX-2, Zalman ZM-STG2 and GlacialStars IceTherm II. The latter is the cheapest of the dozen and costs a mere $5. Each of these is efficient, easy to apply (perhaps, with the exception of the MX-3 and TX3) and remove, and widely available on the market. You won’t be disappointed with any of them. Therefore, we are willing to recommend any of these products and award them with our Recommended Buy title:
The next group includes nine products which cannot boast high thermal conductivity, yet lose only 2 to 4°C to the leaders. Xilence’s X5 and SilverTim, Gelid’s GC-1 and GC-2, the Titan Royal, Arctic’s Matrix and Silver 5, Evercool’s Cruise Missile and Coolink’s Chillaramic are going to satisfy users who are not into overclocking. Most of them are cheap and can be recommended for day-to-day use.
The losers of this test session are the Xigmatek PTI-G3606, Deepcool Z9 and Thermaltake TG-2. The latter is 12°C worse in comparison with the leader under the ideal test conditions. However, this difference shrinks to only 5-6°C when one or both surfaces are far from ideally flat. I can also note that each of these three thermal greases has a rather liquid consistency.
Winding up this review, I want to remind you that thermal interface is not meant for smoothing out uneven surfaces or filling in any cavities between them. It is only meant to ensure efficient heat transfer between two smooth and flat surfaces by filling various microscopic irregularities. Therefore the layer of thermal grease should be as thin and uniform as possible. You should spread out your thermal grease among the area of contact rather than rely on the cooler’s pressure and the fluidity of the thermal grease itself. It is such trifles that help achieve maximum cooling efficiency at overclocking.
In the second part of our roundup I will discuss about 20 thermal greases that come together with various air-based coolers and will compare them with one of the leaders of today’s tests.