-ed.iŋ adjective
Etymology: therm- + setting, present participle of set (become solid)
: having the property of becoming permanently hard and rigid when heated or cured : capable of changing from a plastic or fusible state to an infusible or insoluble state by a chemical reaction effected by heat or other means and leading to a complex high polymer
the phenol resins and plastics were the original synthetic thermosetting materials
— compare thermoplastic