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Resin Comparison: A More In Depth Look at Resin Differences.

Resin Comparison:  A More In Depth Look At Resin Differences.


  • A majority of fiberglass parts are constructed of polyester resin.
  • Good general purpose resin.
  • Excellent for most repairs.
  • Provides a repair that has similar strength & flexural characteristics to the original part.
  • Tolerant of temperature and catalyst variations during lay-up.
  • Wets out fabrics quickly and easily.
  • Isothalic polyester resin is more water & heat resistant than orthothalic polyester resin.


  • Exhibits higher strength characteristics than orthothalic resin.
  • About 90% repairs on a fiberglass boat can be made with this resin.
  • May be used for molds because of its better abrasion resistance and heat tolerance.
  • Has better UV and water resistance.
  • More corrosion resistant than orthothalic polyester resins.
  • Has greater impact resistance due to its increased strength and flexibility.
  • May be used for underwater repairs.


  • Stronger and more durable than polyester resin.
  • Most professional repairs are done in vinylester.
  • Makes strong stiff laminates.
  • Excellent bond strength to sanded laminate and core materials.
  • Will bond to epoxy resin.
  • Higher resistance to chemical, water and UV than polyester resin.
  • Higher resistance to vibration and shock loads.
  • Due to its higher strengths it has better tensile and flexural characteristics
  • Highly resistant to water absorption that causes osmotic blistering that can occur with polyester resins.


  • Has higher ultimate strength than polyester or vinylester resins.
  • Adheres well to wood, aluminum & steel.
  • Excellent for covering wood with fiberglass.
  • Can be thickened with additives to make a wood glue or a structural putty to replace rotted wood.
  • Has electrical insulation properties.
  • Has the strongest bond with carbon and kevlar reinforcements.
  • Has better flexibility than polyester or vinylester.
  • Can withstand substantial impact without cracking.
  • Higher resistance to to environmental and thermal degradation than polyester.
  • Has lower shrinkage than polyester or vinylester resins.
  • Epoxy laminate generally requires much less labor to fair.

All three resins have their own unique roles to play in fabrication and repairs. 

  • How do they compare in cost?
    • Epoxy is the most expensive, Polyester is least expensive & Vinylester is in the middle of the two.
  • What materials work with these resins?
    • Epoxy adheres to carbon fiber and kevlar better than vinylester or polyester.
    • Epoxy is also the best choice for laminating over wood.
  • Over 95% of all boats, truck & car bodies are made of E-Glass(orthothalic polyester resin and isothalic gelcoat)
    • Polyester or vinylester are much better to use than epoxy for polyester fiberglass repairs.
    • Generally on the scale of strength, water resistance and bond strength, Epoxy and Vinylester are the best, Isothalic Polyester is in the middle and Orthothalic Polyester is the weakest.
    • Vinylester may also be used over polyester resin to help prevent osmotic blistering.



This Post Has One Comment
  1. Looking for something to repair a stringer and transom. The wood is dry but rotted. Looking to inject a resin and bind what is therer

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