Surface energy is the degree to which the adhesive and the material's surface repel or attract. The lower the surface energy of an application material the harder adhesion becomes, resulting in labels peeling or falling off altogether. Typical low surface materials include; PVC, Acrylic, Polyethylene, Polypropylene and PTFE Fluoropolymer (Teflon). The higher the surface energy of the application material, the easier the label will stick. Typical high surface materials include: Copper, Stainless Steel, Aluminium, Zinc, Tin, Glass, Nylon, Polyester (PET), ABS Plastic, Polycarbonate.