Many plastics are hydrophobic and are not naturally "wettable". As a general rule, acceptable adhesion is achieved when the surface energy of the solid substrate (measured in dynes/cm) is approximately 8-10 dynes/cm greater than the surface tension of the liquid. Table 1.0 shows typical surface energies for untreated polymer substrates. Due to the vast differences between resin formulations, the values listed below should be used for general benchmark purposes.