Resin infusion and prepreg are two of the most widely used processes for creating high-performance composites. Both techniques can be used to manufacture strong, lightweight and reliable components, but they differ in terms of setup, material handling and application.
Understanding these differences is key when selecting the right process for your project.
Resin infusion is a closed-mould composite manufacturing process in which dry reinforcement materials, such as glass, carbon or aramid, are laid into a mould, covered and sealed by a flexible membrane (typically a disposable film vacuum bag) and then impregnated with liquid resin. Once infused, the resin cures to form a solid composite part.
This method is valued for its ability to produce high-quality, void-free laminates while maintaining a cleaner, safer work environment compared to traditional open-mould processes.
Our direct infusion process takes the principles of resin infusion a step further by automating and refining resin delivery with advanced resin infusion machines. These can enhance control, consistency and efficiency – ideal for both R&D and large-scale production.
Resin infusion provides numerous compelling benefits that make it a top choice for a range of high-performance applications.
Potential drawbacks are typically seen when resin infusion is run as a largely manual process — in such cases, start-up investment, cure duration and operator dependence can be higher. However, when infusion is executed in a controlled, automated RTM/infusion environment with defined envelopes, degassing and process traceability, those limitations are largely removed and the route can equal or outperform prepreg workflows on repeatability, waste and scalability.
Resin infusion is widely used for large or complex structures where cost, integrity and scalability are key considerations and must be balanced. Common applications include:
The benefits offered by resin infusion make it a desirable option for industries that demand efficiency and reliability at scale.
Prepreg, short for pre-impregnated, is a composite manufacturing process where reinforcement fibres are pre-impregnated with a partially cured resin. The materials are stored at low temperatures to prevent total curing before being laid up in a mould (by hand or machine) and cured under heat and pressure, usually by way of autoclave.
This pre-impregnation process provides precise resin content and uniformity across the laminate, ensuring consistent parts and easy handling.
The prepreg process offers several distinct advantages.
On the flip side, prepreg-based routes can carry notable constraints. Material and tooling costs are typically higher, cold-storage is mandatory, and scaling requires specialist infrastructure, most notably autoclaves with associated energy, footprint and compliance overhead. This capital intensity and infrastructure dependency can make prepreg less suitable for large-scale, cost-sensitive or space-constrained programmes compared with non-autoclave liquid moulding approaches
Thanks to its versatility, prepreg is widely used across industries where precision, performance, and reliability are paramount.
These applications benefit from the consistency, high mechanical performance and aesthetic finish offered by prepreg.
Ultimately, neither resin infusion nor prepreg is universally ‘better’ – they solve different programme problems.
In practice, controlled infusion is the stronger choice for most large or serial composite structures because it delivers high precision with lower waste, no cold-store burden and no autoclave dependency, while remaining easier to industrialise at scale and across multiple sites.
Prepreg retains an advantage mainly where legacy qualification paths or extremely narrow tolerance bands on small, high-end parts justify its higher cost and infrastructure demands.
Hybrid strategies are increasingly adopted, using prepreg only where its historic certification or niche tolerances are decisive, and applying infusion where its industrial, economic and resilience advantages dominate.
At Composite Integration, we routinely support organisations transitioning from prepreg-centric assumptions to precise, digitally controlled liquid moulding – integrating degassing, conditioning, traceability and repeatable injection logic to achieve production-grade precision without autoclaves. Whether you need process selection, industrialisation or deployment support, our focus is not just making the part, but making it repeatable, auditable and defensible at production scale.
To reduce cost per part, de-risk production, and move toward scalable high-precision liquid moulding, get in touch.