Epoxies generally out-perform most other resin types in terms of mechanical properties and resistance to environmental degradation, which leads to their almost exclusive use in aircraft components. As a laminating resin their increased adhesive properties and resistance to water degradation make these resins ideal for use in applications such as boat building. Epoxies differ from polyester resins in that they are cured by a ‘hardener’ rather than a catalyst. Since the hardener molecules ‘co-react’ with the epoxy molecules in a fixed ratio, it is essential that the correct mix ratio is obtained between resin and hardener to ensure that a complete reaction takes place. If they are not mixed in the correct ratios, unreacted resin or hardener will remain within the matrix which will negatively affect the final properties after cure.