The curing agent for unsaturated polyester resin is a peroxide that initiates resin crosslinking under the action of accelerator or other external conditions, also known as initiator or catalyst. The "catalyst" mentioned here is different from the traditional "catalyst". In the traditional sense, the term "catalyst" helps the reactants. They promote the reaction without consuming it. In the UPR curing reaction, the peroxide must change its structure before it "catalyzes" the reaction. Therefore, for the peroxide used in the UPR curing, a more appropriate name should be called "initiator" Or "initiator". When it comes to peroxides, the two concepts we need to understand are active oxygen content and critical temperature. Among them, "active oxygen" or "active oxygen content" is a concept that has a close relationship with the curing agent and is often misunderstood.