Unsaturated Polyesters are formed by polycondensation reaction and dicarboxylic acids. Properties of the final cured UP resin can be influenced by variation of the raw materials, utilized for the unsaturated polyester (e.g. toughness, chemical resistance, strength, reactivity, degree of crosslinking). The unsaturated polyesters are mixed with unsaturated monomers, e.g. styrene, yielding the UP resin. The styrene content of common UP resins is 30 % - 40 %. A too high styrene content will lead to a decrease of strength in the cured final part. UP resins are cured with free radicals, resulting from decomposition of organic peroxides [Pergan2016].