Polyester resins are translucent viscous liquids used either alone or in combination with reinforcing fabrics for the production of composite reinforced structures. Polyester resins are thermosetting materials (thermosetting plastic or thermoset), i.e. are petrochemical materials that harden irreversibly. Hardening can occur by heating, generally at high temperature up to 200 ° C (392 ° F), through chemical reaction, or by suitable irradiation. These thermosetting materials are typically liquid before hardening. When a thermosetting resin is cured it cannot be reheated and melted in another format.
Polyester resins, applied either into molds or externally to existing structures to strengthen them and are designed to be molded, laminated or used as adhesives.