Thermal interfacial materials (TIMs) are thermally conductive materials, which are applied to increase thermal conductance, they increase the efficiency in which heat is transferred from the semiconductor to the heat sink. Without using a TIM, microscopic gaps between the component and the heat sink are normally filled with air which is a very poor conductor. Simply stated, TIMs fill these air gaps to improve thermal conductance. TIMs are often chosen based on the size of gaps needing to be filled. Thermal compound, also known as thermal grease, is excellent for filling small gaps less than 0.05 mm. It also has excellent thermal conductivity properties, often rated at greater than 0.8 watts per meter Kelvin (W/mK). The air in which one breathes is rated at approximately 0.022 W/mK. Thermal pads can be used to fill larger gaps of around 0.05 to 0.1 mm and while easier to apply than thermal grease, the thermal conductivity performance is typically not as great.