Prepreg, resin infusion or RTM: which to choose for your part.
Short answer: autoclave prepreg if the part is structural and every gram counts; infusion if it is large and budget comes first; RTM if you need two finished faces and many identical parts. And hand lay-up for prototypes. Here are the criteria.
Carbodynamic engineering team · Published on
The four processes in one sentence
- Prepreg + autoclave: fabrics pre-impregnated with resin, cured under vacuum, pressure and temperature. Highest quality.
- OOA prepreg: prepregs that cure under vacuum only in an oven. Nearly the same quality, lower cost.
- Infusion: dry reinforcement in an open mold, vacuum bag, and the resin is drawn in on its own. Large, economical parts.
- RTM: dry reinforcement in a closed mold with resin injected under pressure. Two good faces and identical parts.
Decision table
Indicative values; every part is studied individually.
| Criterion | Prepreg + autoclave | OOA prepreg | Infusion | RTM |
|---|---|---|---|---|
| Laminate quality | Highest | Very high | High | High |
| Finished faces | One | One | One | Two |
| Mold cost | High | Medium | Low–medium | High |
| Ideal run | Short–medium | Short–medium | One-offs–short | Medium |
| Part size | Up to the autoclave chamber | Up to the oven | Very large | Medium |
| Material cost | High | High | Medium | Medium |
Questions that help you choose
- Is the part structural or cosmetic? Structural and lightweight → prepreg.
- Do you need a finish on both faces? → RTM.
- How many identical parts? One or a few → hand lay-up or infusion; tens or hundreds → RTM.
- Is it very large? → infusion.
- Will the carbon be visible? → prepreg or RTM with a good mold.
The mold matters as much as the process
In every case, the part is only as good as its mold. We machine molds on 5 axes (up to 8 × 3 × 2 m) and measure them before lay-up. If you do the lay-up, we make your mold; if you want the part, we handle the complete process.
Prepreg and autoclave
3 × 8 m autoclave being commissioned, available per project; today we cure prepreg in an oven.
TechnologiesResin infusion
Large parts with a good fiber-to-resin ratio, without prepreg.
TechnologiesRTM
Closed mold, two finished faces and repeatability in production.
TechnologiesOut-of-autoclave (OOA) prepreg
Prepreg quality with more economical molds and cycles, oven-cured.
Send us your drawing or 3D model, and we’ll bring it to life.
We study your project with the same care you put into designing it, then send you a clear proposal covering process, lead time and price. Only have the physical part? We’ll scan it and take it from there.
What customers ask us most.
Which process produces the lightest parts?
Autoclave-cured prepreg, because it achieves the highest fiber content and the lowest porosity.
Which process is cheapest?
For a few parts, hand lay-up or infusion, because they need simpler molds. For production runs, RTM spreads the cost of its mold over many units.
Can you help us choose?
Yes. With the drawing, the part's application and the quantity, we will propose the process, material and mold.