Composites World has a great article on 'Styrene: Issues and Implications' it's history and the pros and cons of listing on the 12th RoC. To read this article click here. Styrene is already in thermoset resins but additional amounts can be added as a thinning agent to get appropriate viscosity. Styrene is smelly stuff even at only a few parts per million. It's a standard smell that comes with custom industrial fiberglass.