CPU fan thermal grease is a vital substance in ensuring efficient heat transfer between the CPU and the heat sink. It is a type of paste that fills the microscopic gaps and air pockets that exist between the two surfaces.

When applied correctly, the thermal grease significantly improves the thermal conductivity. It helps in dissipating the heat generated by the CPU more effectively. To use it, first, the old thermal grease (if any) should be carefully cleaned from the CPU and heat sink surfaces. Then, a small amount of the new thermal grease is applied evenly on the top of the CPU. It should be a thin and even layer, not too thick or too thin. After that, the heat sink is mounted onto the CPU, pressing down gently to ensure good contact. The thermal grease then fills in the gaps and allows for better heat transfer. Without proper thermal grease, the heat may not be transferred efficiently, leading to increased CPU temperatures and potential performance issues or even damage to the CPU in the long run. So, using the right amount and quality of CPU fan thermal grease is essential for maintaining the optimal operating temperature of the CPU.