Thermal paste

Thermal paste, also commonly called thermal grease, is a conductive substance used to form a seal between two objects to ensure a consistent and thorough transfer of heat. When installing a new heat sink on a computer, for example, you need to clean off the thermal paste residue from the previous heat sink and then add a thin layer of thermal paste onto the new heat sink before tightening it down. This process creates a seal between the hot body of the CPU and the metal of the heatsink where the heat can migrate more effectively than it could through an air gap.