Styrene MonomerStyrene Monomer is commonly used as a reactive diluent (solvent) in vinyl ester or unsaturated polyester resins and gel coats. Typically thinned 2 5% to make them thin enough to spray. Styrene Monomer The curing reaction that transforms a liquid mixture of resin, glass, fillers and other materials into a solid, durable composite product involves the crosslinking of vinyl ester and unsaturated polyester molecules by styrene Methyl ethyl ketone peroxide