An open mold provides a finished and dimensionally accurate surface upon which the lay-up can be placed. Gel coat is usually sprayed first on the prepared surface of the mold. The reinforcement materials are applied on top of the gel coat. This form of molding provides one finished side.

When catalyzed, the resin cures going through a polymerization process transforming the liquefied resin into a solid. The cured resin and reinforcement creates a composite material with mechanical properties that exceed those of the individual components. Two commonly used resins are:

• Phenolic resins – phenolic composites have many desirable performance qualities including high temperature resistance, creep resistance, excellent thermal insulation and sound damping properties, corrosion resistance, and excellent fire/smoke/smoke toxicity properties.
• Polyester resins – these resins offer a balance of properties such as versatility in processing and dimensional stability. Polyesters are popular due to lower cost and ease of handling and processing.