Which resin, used to form glass reinforced plastic (GRP), is stiff and an insulator?

• A. Polyester Resin
• B. Urea Formaldehyde
• C. Epoxy Resin
• D. Phenol Formaldehyde

Answer: (A)

In GRP, the resin used as the binding matrix determines how stiff the material is and how well it insulates against electricity. The typical matrix is an unsaturated polyester resin. When cured, it forms a rigid, crosslinked network that gives the composite its stiffness, while the cured polymer itself is a good electrical insulator. It’s also cost-effective and easy to process, which is why it’s widely used for GRP parts. The other resins have characteristics that make them less suitable for standard GRP: urea-formaldehyde tends to be brittle and less durable in moisture, phenol-formaldehyde is very hard and highly heat-resistant but also brittle and expensive, and epoxy resins, while excellent in strength and adhesion, are more costly and often used where higher performance is required rather than for typical GRP applications.