A plasma treatment unit can also be used as part of a vacuum coater system in order to enhance metal adhesion and/or to improve the substrate's qualities as a barrier against oxygen and water vapor transmission. Here, the surface of the web is hit by plasma just prior to the coating process.

The plasma is formed by applying an electrical voltage to a gas, or combination of gases. In addition to removing moisture and other contaminants, plasma treatment acts to increase the number of nucleation sites by the introduction of polar groups, resulting in a coating with a homogeneous surface morphology and fewer defects.