Coat applied to sensitive substrates to protect them from mechanical damage, the action of chemicals, or from the weather and radiation. By means of plasma engineering, many types of protective coats can be applied. To make in particular plastic surfaces scratch-proof, DLC coats can be applied. By plasma polymerisation, primarily electronic circuits can be completely covered by a protective coat to protect them from moisture or oxidation. Parylene coatings play an increasingly important role as protective coats for electronic circuits. Metals form their own protective layer by forming a thin but hard and stable oxide coat. These oxide coats can also be specifically applied by oxidation in the air or oxygen plasma. On the other hand, oxide layers on metals can be removed by plasma treatment in the hydrogen plasma (also see ⇒ Plasma cleaning).