Polyester Resins

Epoxy resin provides better adhesion, moisture resistance, and flexibility compared to polyester resin. While polyester is more economical and widely used in mass production, epoxy is preferred for high-performance applications, repairs, and situations requiring a strong bond.

Polyester resin is widely used for building and repairing fiberglass boats. It is ideal for laminating fiberglass cloth, molding parts, and creating gelcoat finishes. It’s cost-effective and works well for general-purpose repairs.

No, polyester resin does not adhere well to cured epoxy. However, epoxy can be applied over cured polyester if the surface is properly prepared and sanded.

No, you should not use polyester resin on EPS foam (expanded polystyrene). Polyester resin contains styrene, a solvent that dissolves EPS foam on contact. This reaction will ruin your foam core and release harmful fumes. If you're working with EPS foam, for example, in surfboard shaping or foam core laminates, you should instead use epoxy resin, which is chemically compatible and safe for EPS.

It depends on the area, fabric weight and number of plies. As a guide for hand layup with about 15% waste, one gallon wets out about 11 square feet of three plies of 1.5 oz chopped strand mat, or about 50 square feet of three plies of 6 oz cloth. Mat takes about 3.4 oz of resin per square foot per ply. The resin calculator gives exact amounts for polyester layups.

Yes, polyester resin can be tinted using compatible pigments. This is often done to match gelcoat colors or create custom finishes.

At the standard 1.25% MEKP dose and about 77°F, polyester resin gels in roughly 15 to 30 minutes and cures hard over several hours. Warmer temperatures, thicker pours and more catalyst shorten that, and cold lengthens it, so adjust the MEKP dose for your shop temperature.