Styrene

Styrene is the recommended thinner when using polyester and vinyl ester resins and gel coats. All polyester and vinyl ester resins contain styrene monomer. Thinning resins and gel coats isn't usually necessary, but can be performed for applications where a lower viscosity is desired (spraying or infusing).

Styrene resin thinner is a must if you are planning to spray gelcoat using air equipment. It is recommended when adding styrene, that no more than 5% is added in order to maintain the physical properties of the resin or gel coat.