Surface energy is a physical property of the surface of a material that determines whether an adhesive will make intimate contact. On a material with high surface energy, a liquid will spread out or wet the surface; on a material with low surface energy, the liquid will resist flowing and bead up. An adhesive must wet out the substrate to provide a bond.

To choose the proper adhesive it’s important to understand the surface energies of all the substrates and how well the adhesive will wet out each one. Surface cleanliness is also a factor in how well an adhesive wets out the substrate: some adhesives require a high degree of substrate cleanliness, while for others it is less critical.