Thermal Evaporation involves heating a solid material that will be used to coat a substrate inside a high vacuum chamber until it starts to boil and evaporates producing vapor pressure. Inside the vacuum deposition chamber, even a relatively low vapor pressure is sufficient to raise a vapor cloud. This evaporated material now constitutes a vapor stream which the vacuum allows to travel without reacting or scattering against other atoms. It traverses the chamber and hits the substrate, sticking to it as a coating or thin film.