Polyester resin is a general-purpose resin suitable for a wide variety of applications. Methyl Ethyl Ketone Peroxide (MEKP) must be used as the catalyst to begin the curing process at room temperature. Catalyzation rates can be varied with polyester resins, environmental conditions. In thin laminations or when gel coat is sprayed as a topcoat, the surface may remain tacky and not cure properly if left exposed to the air. To get a complete cure, thin laminations with heat resisting Polyester Film or top coats must contain either styrene wax solution of have a coat of polyvinyl alcohol (PVA) solution sprayed over them to seal out the air. With the former, the wax "floats" to the surface as the resin cures, acting as a barrier to the air. Styrene wax must be sanded off after curing, but PVA can be rinsed off with warm water.
Polyester resins are the most commonly used matrix in the marine and composite industry. These resins are styrene-based, flammable and catalyzed when combined with Methyl Ethyl Ketone Peroxide (MEKP). When working with these resins in large projects it is advised to use gloves and a chemical respirator to protect yourself from the fumes. These resins can be used with any type of fiberglass, carbon fiber or kevlar, as well as used over urethane foam and other sandwich core materials. These resins tend to be fairly rigid when cured and also more brittle than epoxy resins.