Hot melt adhesives exist in solid form and are classified by different types of raw materials. Polyurethane (Polyurethane Hot Melt Adhesive) is a reactive type of hot melt adhesive for the base material. After cooling, there will be a chemical cross-linking reaction. Rubber-based pressure-sensitive hot melt adhesives are mainly used in packaging, labels ,metal back stickers and so on. https://www.deepmaterialcn.com/hot-melt-adhesive.html