Thermal paste is necessary because the edges on the top of the CPU and the bottom of the heatsink are not perfectly flat. When the CPU and heatsink come together, there are microscopic gaps that air is able to get into, which means that the heatsink is not moving away as much heat as it could. Thermal paste fills those gaps to transfer the heat effeciently from the CPU to the heatsink. The illustration below illustrates these gaps and thermal paste's purpose.

Arctic Silver 5 is the next generation of thermal pastes to transfer as much heat as possible from the CPU to the heatsink for the lowest possible CPU temperatures thereby creating a quieter and cooler computer. Tests show that a CPU is cooler by 3-12 degrees Celcius just by using Arctic Silver 5 vs. the standard OEM heat transfer pad. With its unique high-density filling of micronized silver and enhanced thermally conductive ceramic particles, Arctic Silver 5 is optimized for use between modern high-power CPUs and high performance heatsinks.

Features:

Contains 99.9% pure silver: Arctic Silver 5 uses three unique shapes and sizes of pure silver particles to maximize particle-to-particle contact area and thermal transfer.

High-Density: Arctic Silver 5 contains over 88% thermally Conductive filler by weight. In addition to micronized silver, Arctic Silver 5 also contains sub-micron zinc oxide, aluminum oxide and boron nitride particles. These thermally-enhanced ceramic particles improve the compound's performance and long-term stability.

Controlled Triple-Phase Viscosity: Arctic Silver 5 does not contain any silicone. The suspension fluid is a proprietary mixture of advanced polysynthetic oils that work together to provide three distinctive functional phases. As it comes from the tube, Arctic Silver 5's consistency is engineered for easy application. During the CPU's initial use, the compound thins out to enhance the filling of the microscopic valleys and ensure the best physical contact between the heatsink and the CPU core. Then the compound thickens slightly over the next 50 to 200 hours of use to its final consistency designed for long-term stability. (This should not be confused with conventional phase change pads that are used by other OEMs with their heatsinks. Those pads melt each time they get hot then re-solidify when they cool. The viscosity changes that Arctic Silver 5 goes through are much more subtle and ultimately much more effective.)