What Is a Resin Reactor: Types, Design Features and Applications Answering the core question: What is a resin reactor? A resin reactor is a jacketed, agitated, usually stainless steel vessel in which monomers are built into polymer chains by polycondensation or addition polymerisation to produce alkyd, polyester, acrylic, epoxy or polyurethane resins. The operating window depends entirely on the family. Alkyd and polyester resins are polycondensations run at 190-260°C that