Used primarily as a reactive diluent in polymer and resin formulations, ethylstyrene improves processability and reduces viscosity in unsaturated polyester resins. It is favored in fiberglass-reinforced plastics and casting applications due to its lower volatility compared to styrene, offering better handling and reduced odor. It also participates in copolymerization reactions, enhancing the thermal and mechanical properties of resulting polymers. Commonly found in composites, coatings, and adhesives where improved reactivity and resin performance are required.