If you’re into PC building then you’ve probably heard of Thermal Grease. It is the material that’s used between your processor and the heat-sink to help transfer the heat from your CPU more efficiently. Thermal Grease can be found in a variety of forms such as ceramic-based, metal-based and liquid-metal compounds. It is also known as thermal paste, CPU paste or thermal interface material (TIM).

The thermal grease consists of a mix of thermally conductive fillers suspended in a silicon oil or silicone fluid compound. The fillers are formulated to maximize thermal conductivity and minimize electrical conductivity so that it is safe to use with electronics.

In order to be a good thermal grease it must fill the microscopic ridges and valleys that occur between the bottom of a semiconductor chip’s heat spreader and the surface of the cooler. The machine marks on these surfaces tend to be convex or concave and result in air gaps of a few thousandths of an inch. The liquid properties of the thermal grease allow it to penetrate these ridges and fill them in so that there is contact at all points rather than just one point, which would be insulated by a layer of air.

There are two types of thermal grease, conductive and non-conductive. Conductive thermal grease pastes contain high concentrations of metal such as silver or copper. These thermal greases have higher thermal conductivity than non-conductive grease but come with the risk that they may cause short circuits if applied incorrectly.