Polyester resin is composed of a combination of acids, anhydrides, glycols and unsaturated monomers, which chemically react to form a three-dimensional network of polymer chains. It is generally manufactured through a chemical reaction known as polymerization, where unsaturated monomers are linked together under certain temperature and pressure conditions with the help of a catalyst. This process results in a viscous, sticky substance that can be molded or poured into molds to form the desired shape.