Choosing the right carbon fiber manufacturing process is the single most consequential decision in any composite product development program. The process determines not just the part cost — it sets the ceiling on mechanical performance, the floor on defect rate, and the feasible production volume. Prepreg layup, wet layup, and filament winding are the three workhorse processes that cover the majority of industrial carbon fiber production. Each has a distinct profile of strengths and weaknesses. This guide compares them head-to-head across the dimensions that matter for engineering and procurement decisions.
Process Overview: Three Paths to a Carbon Fiber Part
Prepreg (pre-impregnated) processing starts with carbon fiber fabric that has been pre-saturated with epoxy resin at the factory, shipped and stored frozen to prevent premature curing. The fabric is cut, laid into a mold by hand or automated tape laying (ATL), vacuum bagged, and cured in an autoclave or oven at 120–180°C under 3–7 bar pressure. The factory-controlled resin content (typically 35–40% by weight) ensures consistent fiber volume fraction of 55–65% — the key driver of mechanical properties.
Wet layup starts with dry carbon fiber fabric. The laminator mixes resin and hardener on the shop floor, wets out the fabric by hand with a roller or brush, lays it into the mold, and vacuum bags it for room-temperature or oven cure. Resin content depends entirely on operator technique and can vary from 40% to over 60% by weight, driving corresponding variation in fiber volume fraction and mechanical properties.
Filament winding winds continuous carbon fiber tows through a resin bath and onto a rotating mandrel under controlled tension. The winding pattern — helical, hoop, or polar — determines the fiber orientation in the finished part. After winding, the part is cured (oven or autoclave) and the mandrel is extracted. Filament winding is inherently limited to axisymmetric or near-axisymmetric shapes — tubes, pipes, pressure vessels, drive shafts.
Prepreg: Maximum Performance, Maximum Control
Prepreg is the gold standard for aerospace and high-performance industrial applications. The factory-controlled resin content eliminates the largest source of variability in composite manufacturing — the human mixing and wetting step. Mechanical properties are predictable part-to-part, batch-to-batch. A prepreg laminate with 60% fiber volume fraction delivers tensile strength of 800–1,200 MPa and flexural modulus of 70–90 GPa in the fiber direction.
The downsides are cost and logistics. Prepreg material costs 2–4× more than dry fabric plus resin bought separately. It requires frozen storage (−18°C) and has a limited out-life (typically 2–4 weeks at room temperature) before the resin advances and the material must be discarded. Autoclave curing adds capital cost and cycle time. For a 1 m² panel 3 mm thick, prepreg-autoclave processing costs $80–150 in material plus $50–100 in labor and equipment amortization.
Wet Layup: Low Cost, High Variability
Wet layup is the entry-level process. Material costs are the lowest of the three — dry fabric at $15–40/m² plus epoxy resin at $8–15/kg. No frozen storage. No autoclave required (vacuum bagging with oven cure is sufficient for most applications). Tooling can be simple — fiberglass or even MDF molds for prototype and low-volume work.
The trade-off is variability. Resin content varies with operator technique, ambient temperature (which changes resin viscosity), and part geometry (vertical surfaces drain, horizontal surfaces pool). A study comparing 50 wet layup laminates made by 5 different technicians found fiber volume fraction ranging from 38% to 55%, with corresponding tensile strength varying from 400 to 750 MPa. For non-structural or cosmetic parts, this variability is acceptable. For primary structure, it is not.
Filament Winding: The Automation Advantage
Filament winding occupies a unique position — automated enough for production volumes, flexible enough for custom fiber architectures, but limited to rotationally symmetric geometries. A filament-wound tube with optimized winding angles can achieve fiber volume fractions of 60–70% — equal to or higher than prepreg — because the winding tension compacts the fibers during laydown.
The cost structure is attractive for cylindrical parts. Material costs are similar to wet layup (dry fiber plus resin bath). Labor is dramatically lower — one operator can oversee multiple winding machines. Cycle times are fast: a 2-meter tube 50 mm in diameter can be wound in under 10 minutes. The capital cost of a CNC filament winder ($50,000–200,000) is a fraction of an autoclave ($500,000–2,000,000). For tubes, pipes, and pressure vessels at medium to high volumes, filament winding is usually the lowest-cost process.
Head-to-Head: 7-Dimensional Comparison
| Dimension | Prepreg | Wet Layup | Filament Winding |
|---|---|---|---|
| Fiber Volume Fraction | 55–65% (consistent) | 38–55% (variable) | 60–70% (consistent) |
| Tensile Strength (0°) | 800–1,200 MPa | 400–750 MPa | 900–1,400 MPa |
| Part-to-Part Variability | <3% (very low) | 10–25% (high) | 3–8% (moderate) |
| Material Cost (/kg) | $40–90 | $15–30 | $18–35 |
| Tooling Cost | $5K–50K | $1K–10K | $10K–50K (mandrel) |
| Labor Content | Medium–High (layup) | High (all manual) | Low (automated) |
| Cycle Time (per part) | 2–8 hours (autoclave) | 1–4 hours (oven) | 10–60 min (winding only) |
| Geometry Freedom | Excellent (complex shapes) | Excellent (complex shapes) | Limited (axisymmetric only) |
| Void Content | <1% (autoclave) | 2–5% (vacuum bag) | 1–3% (tension + oven) |
| Best Volume Range | 1–5,000/yr | 1–500/yr | 500–50,000/yr |
| Typical Applications | Aerospace, motorsport, premium sporting goods | Prototypes, marine, repair, low-volume industrial | Tubes, pipes, pressure vessels, drive shafts, masts |
How to Choose: Decision Framework by Application
If your part is cylindrical and your volume exceeds 500 units per year, filament winding is almost certainly the right answer — it delivers the best mechanical properties at the lowest unit cost for axisymmetric geometries. If your part has complex curvature and performance is critical (aerospace, structural automotive, premium sporting goods), prepreg is the standard — the cost premium buys predictability and performance that wet layup cannot match.
If your volume is very low (under 100 units), your part geometry is complex, and your performance requirements are moderate, wet layup is the practical choice. The material cost savings fund the extra labor, and the variability is manageable for non-structural applications. One caveat: if your wet layup part later needs to scale to production, you will likely need to re-qualify with a different process. Factor that transition cost into the initial make-vs-buy decision.
The hybrid option — using prepreg for critical structural plies and wet layup for cosmetic or non-structural plies in the same part — is increasingly common in industrial applications. It captures most of the performance benefit of prepreg at roughly 70% of the full-prepreg material cost. This approach requires engineering analysis to verify that the wet layup plies do not become the weak link in the laminate, but when designed correctly, it offers the best cost-performance balance for many industrial applications.
CFRP TSTAR manufactures carbon fiber components using prepreg, wet layup, and filament winding processes — with in-house engineering to help select the right process for your application. From prototype to production, we deliver consistent quality with full material traceability and mechanical testing documentation.
