Thermal greases and phase change materials require a mechanical fixture, usually in the form of a spring clamp or screws. The diagram on the left illustrates a typical thermal grease application, where a heat sink is mounted onto a CPU using screws. Pressure is required for material to wet out and replace any air trapped between surfaces. The higher the pressure or torque applied, the better the material wets the surfaces and dissipates heat. The chart on the top right is actual data showing how the performance of thermal grease and phase change material improves with increased pressure.