Pultrusion

Pultrusion continuously pulls fiber reinforcements through a resin bath and heated die to make constant-cross-section composite profiles at high throughput.

Overview

Pultrusion is a continuous composites process that produces straight, constant-cross-section profiles by pulling fibers (rovings, mats, or stitched fabrics) through resin impregnation and a heated steel die where the laminate cures to final shape. It’s the go-to method for long lengths of consistent geometry: flat bars, angles, channels, tubes, and custom profiles.

Choose pultrusion when you need high volume or long-run production, repeatable mechanical properties along the length, and low cost per meter/foot. Tooling is relatively simple compared with closed-mold processes, and line speeds support large total output.

Tradeoffs: geometry is limited to constant cross-sections with no local bosses, pockets, or varying wall thickness; cut-to-length and secondary machining are common. Fiber architecture is predominantly axial, so transverse strength and complex load paths may require mats/stitched fabrics or hybrid layups. Tight cosmetic requirements, tight feature tolerances, and curved/3D shapes usually push you to other composite methods.

Common Materials

  • E-glass
  • Carbon fiber
  • Vinyl ester
  • Epoxy
  • Polyester
  • Polyurethane

Tolerances

±0.010" to ±0.030"

Applications

  • FRP ladder rails and stiles
  • Fiberglass I-beams and channels for structures
  • Wind turbine blade spar caps
  • Non-conductive tool handles and poles
  • Cable tray supports and walkways
  • Insulated composite rebar

When to Choose Pultrusion

Pultrusion fits parts that are straight, constant cross-section, and needed in long lengths or high quantities. It’s a strong choice when you want consistent fiber alignment and properties along the length with low piece price. Plan on cut-to-length plus secondary operations for holes, end features, and tight interfaces.

vs Resin Transfer Molding

Choose pultrusion when the part can be a constant cross-section profile and you want continuous production with low cost per linear foot. RTM is better for 3D shapes, local features, and varying thickness; pultrusion wins on throughput and length consistency.

vs Vacuum-Assisted Resin Transfer (VARTM)

Choose pultrusion when you need repeatable, automated production of long straight profiles with controlled fiber volume and minimal labor. VARTM is better for large, contoured parts and one-off tools; pultrusion is better for long runs of the same profile.

vs Prepreg Layup with Autoclave

Choose pultrusion when the geometry is simple and constant, and you care more about cost and throughput than aerospace-grade laminate quality. Autoclave prepreg supports complex shapes, premium surface, and tight laminate control; pultrusion delivers high-rate profiles with fewer geometry options.

vs Filament Winding

Choose pultrusion for non-round profiles (channels, angles, flat bars) and for solid or multi-cell shapes that aren’t purely rotational. Filament winding is better for axisymmetric pressure vessels and pipes where hoop strength and controlled winding angles are primary.

vs Compression Molding (Composites)

Choose pultrusion when the part is long and continuous and the business case is cost per length and continuous output. Compression molding is better for discrete 3D parts with molded-in features; pultrusion is better for continuous profiles that you cut and machine afterward.

Design Considerations

  • Keep the cross-section constant along the full length; avoid tapers, bosses, and local thickness changes
  • Call out a realistic cut-to-length tolerance and identify any critical end-squareness requirements
  • Place holes, slots, and end features as secondary operations; define datums and drill/machine allowances
  • Use generous corner radii and avoid sharp internal corners to reduce die wear and fiber wash
  • Specify fiber orientation and minimum fiber volume fraction targets based on load direction (axial vs transverse needs)
  • Provide profile envelope dimensions and straightness/camber requirements over a defined length to support accurate quoting and inspection