Can Unsaturated Polyester Resin Be Used in the Second Layer of Fiberglass Molds?

Yes, you can use unsaturated polyester resin in the second layer of fiberglass molds. However, you need to address the classic issue of resin shrinkage. The best way to manage shrinkage in unsaturated polyester resin is to apply it in multiple layers over several days, allowing each layer to cure fully. This gradual process significantly reduces the shrinkage effects. Alternatively, newer zero-shrinkage mold resins offer negligible shrinkage, enabling completion in a single application that traditionally takes four days or more.