Epoxies are best known for their excellent adhesion, chemical and heat resistance, mechanical properties, and outstanding electrical insulating properties. The chemical resistance of epoxies is excellent against basic solutions (best choice for brine tanks).

Epoxies are more expensive than polyesters, and cure times are longer, but their extended range of properties can make them the cost/performance choice for critical applications.

The epoxy resins are formed by a reaction of an epoxide (like epichlorohydrin) with a hardener or polyamine (like triethylenetetramine) that has tremendous cross-linking to create a very tough and yet stiff polymer. The viscosity of epoxies is another step higher than polyesters or vinyl esters.  Most epoxies start in the range of 900 centipoise.

Attributes of epoxy resins include extremely low shrinkage, good dimensional stability, high temperature resistance, good fatigue and adherence to reinforcements.

Given the extensive double bonding of the resin, normal shrinkage is less than might be expected based on its strength.

Best Processes

Open Molding (Hand Lay-up/Spray-up), SMC/BMC, Resin Transfer Molding (RTM), Filament Winding. The best process for your product is a function of your tooling budget, part specification (such as dimensional tolerance and physical properties) and production volume.


Typically glass, but adheres well to all reinforcements.

Special Design Considerations

Because this material has very low shrink rates, we can assist you with assessing the suitability for your product, as well as tooling considerations. MFG’s Technical Design Guide for FRP Composite Products and Parts provides in-depth information for product designers. You can download it on the bottom of this page.

Technical Details

Surfaces of epoxy resin composites are not cosmetically appealing. This is a best choice for products where strength and toughness are paramount, as the material offers both outstanding flexural and tensile modulus.

Cost Considerations

Cost of epoxies as compared to polyester resins for SMC is about 3X.