When should you use a high-temperature epoxy, BMI or cyanate ester prepreg?
Once a composite application starts reaching higher temperatures, choosing a material becomes more complicated than selecting the resin with the highest service temperature.
High-temperature epoxy, BMI and cyanate ester prepregs can all perform in demanding environments, but they offer different balances of thermal performance, mechanical properties and processing requirements.
How do epoxy, BMI and cyanate ester prepregs differ?
A high-temperature epoxy is often the most practical starting point where it can comfortably meet the required service temperature. Epoxy systems are widely understood, can offer good structural performance and are generally familiar to manufacturers.
SHD's MTC400 and HTC400 are examples of high-temperature epoxy systems for elevated-temperature applications.
BMI systems may be more appropriate when the temperature requirement moves beyond the practical range of epoxy. They can offer higher thermal capability for demanding components and tooling, although they may require higher cure temperatures and more involved processing.
SHD's BMI-1SC is designed for high-temperature tooling and component applications, with a published maximum onset Tg after post-cure of around 350°C.
Cyanate ester systems are often considered when high-temperature performance needs to be combined with specialist properties such as low outgassing or dielectric performance.
SHD's CEM160 offers high-temperature and low-outgassing performance, while the newly launched CEM101 is specifically engineered for applications requiring minimal dielectric constant and loss tangent.
These resin families should not be viewed as a simple progression from epoxy to BMI to cyanate ester. A higher Tg is not automatically better if the additional capability is unnecessary or introduces a more demanding manufacturing process.
What should you compare before choosing a high-temperature prepreg?
Start with the finished component and work backwards - consider:
Expected service and peak temperatures
Mechanical performance required at temperature
Cure temperature and cure time
Post-cure requirements
Available oven, autoclave or press capability
Tooling temperature limits
Toughness and structural requirements
Environmental exposure
Outgassing, dielectric or other specialist requirements
Production volume and manufacturing practicality
If a high-temperature epoxy meets the requirements, it may offer the simplest and most practical route. If greater thermal capability is needed, BMI may be more suitable. Where high temperature must be combined with properties such as low outgassing or dielectric performance, cyanate ester may be worth considering.
The final choice should be based on the complete operating and processing requirements, not the resin family or Tg alone.
How do SHD's high-temperature prepregs compare?
The products below are examples rather than a product-selection chart:
MTC400
A toughened high-temperature epoxy for elevated-temperature structural applications.
HTC400
A higher-temperature epoxy option for applications requiring greater thermal capability.
BMI-1SC
A BMI system for demanding high-temperature tooling and component applications.
CEM160
A cyanate ester system combining high-temperature performance with low-outgassing characteristics.
CEM101
A cyanate ester system for applications requiring minimal dielectric constant and loss tangent.
SHD offers a wider range of prepreg systems and the most suitable option will depend on the application, reinforcement, processing route, loading and service environment. Highlighting a specific product does not mean it is the only possible solution.
Need help choosing between epoxy, BMI and cyanate ester?
Let us know the temperatures your component needs to handle, how you plan to manufacture it and the key performance requirements, and our technical team will help you compare the available options and identify suitable materials for further evaluation.
