What Resin Is Best for Making Fiberglass Molds?

Almost any polyester resin can be used for fiberglass mold making, but the choice depends on the final part’s requirements.

The best resin may not always be the most suitable. Mold making involves balancing mold performance, material costs, and production time. Whether you’re making molds for personal use or for others, aim to meet the actual needs at the lowest manufacturing cost.

Common Resins for Fiberglass Molds:

  • Epoxy Mold Resin
  • Vinyl Ester Mold Resin
  • Unsaturated Polyester Resin
  • Zero Shrink Mold Resin (available in both unsaturated and vinyl ester systems)

Choosing the right resin depends on your specific needs. Here are some examples:

  1. Making Molds for Epoxy Parts (e.g., Drone Shells): Epoxy parts often require heat curing, sometimes up to 130°C. In this case, epoxy mold resin is the best choice to ensure durability and high-temperature stability. For small batches (e.g., 20 pieces), a cost-effective option is high-temperature-resistant vinyl ester gel coat paired with vinyl ester resin.
  2. Conventional Hand-Layup Fiberglass Molds (e.g., Train Interiors, Fan Housings): Vinyl ester gel coat and vinyl ester mold resin are traditional and effective. For molds requiring high dimensional accuracy, zero shrink mold resin can be used to achieve better shrinkage control.
  3. Large Hand-Layup Molds (e.g., Fiberglass Yacht Molds): For large molds, cost-effective unsaturated polyester resin is the preferred choice due to the high expense of standard mold materials.