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Difference between epoxy resin and polyester resin

The easiest way to answer the question of whether polyester resin or epoxy resin is to compare the advantages and disadvantages of polyester resin and epoxy resin and show the different areas of application of the two:

Polyester resin

Advantages of polyester resin over epoxy resin

  • Easy handling and processing, since the addition of hardener is variable in a certain ratio. As a rule, the addition of hardener is between 1.5-2.5%. The amount of hardener is specified by the manufacturer of the polyester resin. However, caution is advised. Adding hardener to the polyester resin that exceeds the technical specifications leads to embrittlement of the component, whereas a smaller amount than specified leads to non-through-hardening.
  • Polyester resin is cheaper than epoxy resin.
  • Polyester resin can be easily processed with glass fiber mats, since the binder in glass fiber mats is dissolved by the styrene contained in polyester resin.

Disadvantages of polyester resin compared to epoxy resin

  • Strong odor (especially when curing) due to the styrene contained in the polyester resin. High-quality polyester resins (e.g. Resinpal 1705) contain skin-forming agents that reduce styrene emissions. Styrene-reduced polyester resins that have been developed in recent years partially eliminate this disadvantage.
  • Polyester resin generally has less pronounced mechanical properties than epoxy resin. This only applies in combination with reinforcing fibers and does not apply to the pure synthetic resin itself.
  • Polyester resin has less adhesive properties than epoxy resin, e.g. on metal.

Epoxy resin

Advantages of epoxy resin over polyester resin:

  • Compared to polyester resin, epoxy resin combined with reinforcing fibers has more pronounced mechanical properties.
  • Epoxy resin shrinks less than polyester resin when cured. This property is particularly important in toolmaking, mold making and the construction of very high-quality components.
  • Epoxy resin is usually odorless and can therefore also be used indoors.
  • Epoxy resin has excellent adhesive properties (e.g. on wood and metal). The good adhesive properties are also reflected in strong fiber adhesion. This is one of the reasons for the higher mechanical properties of epoxy resin compared to polyester resin.
  • Epoxy resin has a high hydrolysis resistance and is far more resistant to osmosis than polyester resin, making it well suited for GRP parts that are exposed to water (e.g. boats).

Disadvantages of epoxy resin compared to polyester resin:

  • When mixing, the exact ratio of epoxy resin to epoxy hardener should be observed. Excessive addition of hardener leads to embrittlement of the component, while adding too little hardener impedes through-hardening.
  • Epoxy resin is more expensive than polyester resin.
  • Epoxy resin can only be processed to a limited extent with glass fiber mat. The reason is that fiberglass mats contain a binder that is dissolved by the binder in the styrene. It is therefore recommended that epoxy resin is always processed with glass filament fabric, glass fiber fabric or carbon fabric.