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 are not usually necessary but can be performed for applications where a lower viscosity is desired (spraying or infusing). Fibre Glast recommends adding styrene at no more than 5% to maintain the physical properties of the resin or gel coat

Styrene thinner, also known as styrene monomer, is a commonly used solvent in composite manufacturing processes. Here is some information about the use of styrene thinner in composites:

1. Dilution of Resins: Styrene thinner is used to dilute and adjust the viscosity of polyester and vinyl ester resins. By adding styrene thinner, the resin becomes more fluid and easier to handle, allowing for better wetting out of reinforcement materials and improved flow during infusion or casting processes.
2. Solvent for Resin Cleanup: Styrene thinner is used as a solvent for cleaning and removing uncured resin from tools, equipment, and surfaces. It can dissolve and help remove excess resin, making it easier to clean up after composite fabrication.
3. Adjusting Resin Properties: The addition of styrene thinner can affect certain properties of the resin system. It can increase the resin's flexibility and improve its wetting characteristics, enhancing the impregnation of reinforcement materials. However, excessive use of styrene thinner can lead to reduced mechanical strength and increased shrinkage of the cured composite. It is recommended to use no more than 5% by weight.
4. Safety Considerations: Styrene thinner is a volatile organic compound (VOC) and should be handled with caution. It has a distinct odor and can release harmful fumes. It is important to work in a well-ventilated area or use proper ventilation systems to minimize exposure. Personal protective equipment, such as gloves and goggles, should be worn when handling styrene thinner.
5. Flammability: Styrene thinner is highly flammable and should be stored and handled away from open flames or sources of ignition. It is important to follow proper safety practices to prevent fire hazards.

It is important to note that the specific use and concentration of styrene thinner can vary depending on the resin system, process requirements, and environmental regulations. Always follow the guidelines and recommendations for the appropriate use, handling, and disposal of styrene thinner in composite applications.