These chemicals are used only when necessary to dilute the resin, i.e. to reduce its viscosity. Polyester resins contain approximately 30-50% monomers. They are used in the production of certain materials to bring the resin into the appropriate viscosity range.
While styrene is the most commonly used monomer, other monomers such as methyl methacrylate (MMA) and vinyl toluene (VT) are also used for different purposes.
We do not recommend adding monomers to any ready-to-use product as it will affect the overall performance and curing properties of the material. Added monomer is known to have adverse effects on the product.