If additive-free plastic materials cannot or can only poorly be bonded or coated in spite of a clean surface, this is most probably due to their low polarity and the resultant low surface energy. Surface energy is the amount of energy required for breaking chemical bonds when producing new material surfaces. It is the most important measure for assessing the probable adhesion of an adhesive layer or coating. In general, plastic materials have low surface energy, usually between <28 dyne and 40 dyne. Experience, however, has shown that good prerequisites for adhesion are first achieved with surface energies greater than 38-42 dyne. For liquids, the surface energy is equal to the surface tension, and each liquid, paint and adhesive has its own inherent tension. Secure coating adhesion is conditional on the surface energy of the solid material (substrate) being higher than the surface tension of the liquid adhesive or paint. There are several methods for increasing the surface energy, the most frequent being the use of solvent-containing and thus environmentally harmful substances.