Although five major bonding mechanisms are associated with adhesion promotion, two primary factors predominately influence the adhesion of any type of polymer to another substrate: chemical surface-to-surface interaction at the molecular level, and the wettability of the adhesive so as to enable surface spreading. Adhesion values can also be influenced by the matrix, or vehicle, that enables surface wet-out.
For example, extrusion-coated, water- and solvent-based, and energy-curable adhesives all wet to a surface at different rates. This rate of wettability can be influenced by the surface condition, including the concentration of migrated or deposited contaminants, the concentration of oxides, surface tension level, etc. These factors also directly or indirectly impact adhesion values.