Adhesives can be classified in several ways, including their material origin (e.g., natural or synthetic) and their type of cure (e.g., physical curing such as drying or chemical curing). Terms such as thermoset, thermoplastic, structural, or non-structural are also used in the industry.
The term thermoset historically meant adhesives that cured or “set” on heating. The oldest type of this adhesive are the so-called PF, UF, and MF resins (phenol formaldehyde, urea formaldehyde, and melamine formaldehyde, respectively), which are commonly used to make plywood and are cured using heat and pressure.