Strong structural bonds are formed using polyurethane reactive hot melt glue (PUR), which cures as it reacts with air. The glue quickly creates a bond with epoxy-like strength. The PUR hot glue's tensile strength for the first two days keeps increasing. In contrast to regular hot glue, the glue is more UV resistant. You can add weatherproof, dustproof, insulating, and temperature change resistance. PUR, however, comes with specialized PUR hot melt guns and is usually sold in tubes. It is significantly more expensive and has a shorter shelf life.