Towpreg vs Prepreg: Differences in Material Form and Processing.
Both are pre-impregnated fibre, but they are made differently, behave differently in an AFP head and suit different programmes.
Starts as a sheet of unidirectional prepreg made on a prepreg line. The sheet is then slit into narrow tapes of controlled width and wound onto spools for the placement head.
Made by impregnating a single fibre bundle directly with resin and winding it at a constant width, without a sheet stage. The tow is the product.
Why the Route Matters.
Slitting a sheet gives tight width control and well-defined edges, which helps an AFP head place tows edge to edge. Patent literature describes slit tapes produced across a wide range of widths, with AFP tapes commonly in the region of a few millimetres to around 25 mm.
Towpreg avoids the sheet and slitting steps, which is the main reason it attracts interest: industry sources describe it as lower cost than conventional thermoset unidirectional slit prepreg.
How They Behave in an AFP Head.
Width tolerance
Towpreg typically has looser width tolerances. Width variation feeds directly into gaps and overlaps between adjacent tows.
Stiffness and feeding
Towpreg tends to have lower stiffness. Reliable feeding through guides, cutters and rollers depends on stiffness and width consistency.
Tack and unwinding
Tacky towpreg wound on a bobbin can stick to itself as it unwinds, producing fuzz and fibre bridging that degrade layup quality.
Edge quality
Slit edges are cut through the fibre; towpreg edges are formed by the bundle itself. Each has different fuzz and fraying behaviour in the head.
Questions to Ask Before Choosing.
- Which forms and widths does the placement head accept?
- What width tolerance can the layup strategy absorb?
- Is the resin system qualified for the application?
- What are the storage, shelf-life and out-time limits?
- How will tack be managed across the layup speed range?
- What batch traceability and certificates come with the material?
- How sensitive is the part cost to material price?
- Does the customer specification name a qualified material?
Match the Material to the Head and the Part.
Neither form is better in general. The right choice is the one the equipment can place consistently, the qualification route accepts and the programme can afford.
DANTA selects material forms against the installed head configuration and publishes supplier names and grades only after supply and approvals are confirmed.
- US Patent 10,934,406. Prepreg tape and use thereof. United States Patent and Trademark Office.
- US Patent 12,146,039. Resin composition for carbon fiber composite material, towpreg. United States Patent and Trademark Office.
- US Patent 9,630,390. Method of manufacturing curved composite structural elements. United States Patent and Trademark Office.
- US Patent 11,421,091. Method for manufacturing prepreg, coating device, and apparatus for manufacturing prepreg. United States Patent and Trademark Office.
- Mikrosam (2025). Towpreg manufacturing for scalable performance and precision. JEC Composites feature.
Technical articles are general information. They do not replace application-specific engineering analysis, qualified professional advice or approved manufacturing instructions.
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