The gist of it:
Thermal compound is a creamy or liquid substance used to fill in microscopic gaps and interstices between two surfaces, especially metal ones. The goal is to maximize the amount of surface area that actually contacts each other to improve heat transfer from one to the other. It’s used in electronics, like computers and video cards, to help them get rid of the excess heat generated during operation.
In our tests, we found that good traditional pastes can come pretty close to the best liquid metal compounds in terms of temperature load averages. That’s despite the fact that the latter are usually worlds apart in price-per-gram terms.
Liquid metal compounds also require more focus and attention when applying them because they’re electrically conductive, so if you apply too much or get any in the wrong spot it could fry your computer.
As a result, you need to be more careful when using them, especially if you’re new to DIY computing or don’t have a lot of experience with it. It’s easy to get the stuff everywhere other than where you want it to go, and even if you managed to avoid that, movement of the CPU cooler or case could wreak havoc by leaving ugly lumps and ridges of thermal grease in the gap between processor and cooler.
Fortunately, most modern thermal compounds have a much better chance of being able to stay put than their ancestors. The best are thick, pliable, have good stability on application and clean up well, making them a popular choice for builders.