Prepreg is a ready-to-mold composite material: reinforcement fabric or unidirectional fiber pre-impregnated with resin, kept in a controlled (usually refrigerated) state. It removes the messy resin-mixing step from your workshop and gives you consistent, repeatable parts. But choosing the wrong prepreg can waste money and time. Here is what actually matters.
1. Thermoset vs thermoplastic prepreg – the first decision
The single biggest choice is the resin family:
Thermoset prepreg (epoxy, phenolic, BMI): cured by heat into a permanent cross-linked network. Pros – excellent mechanical properties, good temperature resistance, well-established processing (vacuum bag, autoclave, hot press). Cons – must be stored cold (-18°C), has a limited out-life, cannot be reshaped or recycled, longer cycle times.
Thermoplastic prepreg (PP, PA, PPS, PEEK with continuous fiber): the polymer solidifies by cooling, no chemical cure. Pros – unlimited shelf life at room temperature, can be thermoformed and welded, recyclable, very short cycle times (minutes), high impact toughness. Cons – needs higher processing temperatures and pressures, generally higher material cost, fewer “drop-in” processing shops.
2. Key parameters to specify
Resin content (RC): typically 30–45% by weight for epoxy prepreg. Higher resin content improves tack and surface finish; lower content reduces weight but makes handling harder.
Fiber areal weight (FAW): the weight of fiber in one layer (e.g. 125, 200, 300 gsm). Choose to match your target laminate thickness and fiber volume fraction.
Tack level: how sticky the material is. High tack helps complex lay-ups; low tack is easier to handle in automated cutting. Specify according to your process.
Volatile content and void control: for aerospace and structural parts, choose low-volatile grades processed under vacuum or autoclave to keep porosity low.
Out-life and shelf life: thermoset prepreg must be used within its out-life window at room temperature and within shelf life under cold storage – always check the supplier’s data sheet.
3. Match the prepreg to your process
Autoclave / vacuum bag: standard thermoset prepreg, aerospace-grade, low void content – maximum quality.
Hot press / compression molding: fast-cure thermoset prepreg or thermoplastic prepreg – high productivity for automotive and industrial parts.
Thermoforming: thermoplastic prepreg (CFRTP) – seconds-to-minutes cycle, recyclable, great for consumer and semi-structural parts.
Out-of-autoclave (OOA): low-pressure curable grades for tooling and prototypes without an autoclave.
4. Storage, transport and handling
Thermoset prepreg is a living material: it cures slowly even at room temperature. Keep it at -18°C for storage, transport it in insulated containers, and track the accumulated out-life from the moment it leaves cold storage. Thermoplastic prepreg is far more forgiving – it can be stored and shipped at room temperature, which simplifies logistics and reduces scrap for small and medium users.
5. Quick decision table
Need maximum mechanical performance + have autoclave → thermoset epoxy prepreg, aerospace grade.
Need fast cycle + high volume + recyclable parts → continuous fiber thermoplastic prepreg.
Need excellent surface + medium volume → thermoset prepreg with fine 3K fabric, fast-cure resin.
Budget-sensitive + room-temperature logistics → thermoplastic prepreg or dry fabric + infusion.
6. How to order
A complete prepreg specification includes: reinforcement (fabric weave and tow size, or UD), fiber areal weight, resin type and content, tack level, curing temperature/time, roll width and required shelf life. LX Composites supplies both thermoset and thermoplastic prepregs with carbon, glass and aramid reinforcements, custom resin systems and areal weights. Tell us your process (autoclave, hot press or thermoforming) and we will recommend the right grade – contact us for samples and data sheets.
Related Reading
- Prepreg Storage & Shelf Life — Storage conditions, out time and how to spot expired material
- Carbon Fiber Fabric Selection Guide — Tow size, weave, weight and width
- CFRT Production & Applications — Continuous fiber thermoplastic composites explained
Related Products
Thermoplastic Prepregs · Thermoset Prepregs
Have a specification to match? Send us the application and process through our contact page and we will confirm what we can supply.