FRP Guides

What Is Pultrusion? The FRP Process Explained Step by Step

In short: Pultrusion is a continuous manufacturing process for composite profiles with a constant cross-section. Glass fiber rovings and mats are pulled from creels, wetted with thermoset resin, shaped, and drawn through a heated steel die where the resin cures. Pullers grip the finished profile and a saw cuts it to length. The name combines "pull" and "extrusion". Pultrusion makes FRP I-beams, channels, angles, tubes, handrail components, ladder rails, cable tray rails and pultruded grating bars. Most fibers run lengthwise, so pultruded parts are strong and stiff along their length.

What Is Pultrusion? The FRP Process Explained Step by Step – In short summary: key points at a glance

Table: Materials used – What Is Pultrusion? — Materials used. Summary diagram of the table in this guide.

The pultrusion line, station by station

Diagram: Advantages – What Is Pultrusion? — Advantages: summary diagram from this guide.

1. Creel and mat racks

Hundreds of roving packages are mounted on a creel. Rolls of mat or stitched fabric are mounted nearby. Rovings provide lengthwise strength. Mats and fabrics provide transverse strength so the profile doesn't split along its length.

2. Resin impregnation

Fibers are wetted out in an open resin bath or a closed injection box mounted at the die entrance. The resin mix includes catalyst (initiator), fillers, pigments, release agent and, where specified, UV inhibitors and fire retardants.

3. Preforming

Guide plates gradually bring the wet fibers into the approximate shape of the final profile, place the mats and veils correctly, and squeeze out excess resin.

4. Heated die

The heart of the process. A precision steel die, often chrome-plated, has the exact cross-section of the profile. Heating zones along the die raise the temperature so the resin gels and cures as the material passes through. Die design and temperature profile are critical to quality.

5. Pulling system

Caterpillar-track or reciprocating hydraulic clamp pullers grip the cured profile and pull it steadily. Line speed is set by the profile size, resin system and cure.

6. Cut-off saw

A flying saw moves with the profile and cuts it to the programmed length without stopping the line.

Materials used

Material	Role
Glass roving	Lengthwise strength and stiffness
Continuous filament mat / stitched fabrics	Transverse strength and crack resistance
Surface veil	Resin-rich surface, corrosion and UV protection
Polyester or vinyl ester resin	Matrix; sets chemical resistance
Fillers, pigments, additives	Color, fire retardancy, shrinkage control, UV protection

See Polyester vs Vinyl Ester vs Phenolic Resin.

Diagram: Limitations – What Is Pultrusion? — Limitations: summary diagram from this guide.

What pultrusion can make

Structural shapes: I-beams, wide-flange beams, channels, angles, square and rectangular tubes, round tubes, rods and flat sheet. See FRP Pultruded Profiles Guide
Handrail rails and posts. See FRP Handrail Systems Guide
Ladder rails and rungs. See FRP Ladders and Cage Ladders
Cable tray side rails and rungs. See FRP Cable Tray Guide
Grating bearing bars. See Molded vs Pultruded FRP Grating
Purlins, cooling tower structural members, fence posts and tool handles

Advantages

Continuous and efficient: long production runs with consistent quality
High fiber content and controlled fiber placement give a good strength-to-weight ratio
Any length within transport limits
Consistent dimensions set by the die
Color through the profile, with no painting needed for corrosion protection

Limitations

Constant cross-section only. Tapered or curved parts need other processes.
Die cost. A new die is an upfront investment, so pultrusion suits repeat or larger quantities.
Anisotropy. Transverse strength is lower than longitudinal strength, which affects connection design.
Lower stiffness than steel, so design is usually governed by deflection.

Developing a custom profile

Concept: you send a drawing or describe the function, loads and environment.
Engineering review: we check wall thickness, radii, fiber architecture and feasibility.
Die design and manufacture.
Trial run and samples: dimensional checks and, where required, testing.
Production with agreed tolerances and inspection.

Design tips: keep wall thickness as uniform as possible, use generous internal radii, and avoid very thin, unsupported flanges.

Quality checks

Typical checks include dimensions against the drawing, appearance (dry fibers, cracks, surface defects), and Barcol hardness as an indicator of cure. Mechanical tests are carried out where specified. European projects may specify EN 13706 grades for pultruded profiles.

Customization

FIBROVX runs pultrusion for standard and custom profiles. We can produce new dies, select resin and veil systems, pigment colors, cut and machine parts, and supply OEM marked products. See our FRP pultruded profiles and FRP purlins.

Need a quote or a drawing check?

FIBROVX manufactures FRP products in our own factory in China and builds every item to order: sizes, resin system, color, molds and OEM branding. Send your application, dimensions or drawing, quantity and destination port.

Request a Quote

Pultrusion compared with other processes

Pultrusion is not the only way to make FRP parts, and choosing the right process matters:

Molding (for molded grating) builds a grid with fibers in two directions and a higher resin content. It suits panels that need bidirectional strength and many cut-outs.
Filament winding wraps fibers around a mandrel and suits round, pressure-bearing products such as tanks and pipes.
Hand lay-up suits one-off or complex shapes such as covers, hoods and custom fittings.
Pultrusion suits long, straight parts with a constant cross-section, produced continuously in large quantities.

See How FRP Is Made for a full comparison.

Information to send for a pultruded profile quote

Drawing or sketch of the cross-section, with dimensions and wall thickness
Length per piece and total quantity
Resin requirement (general purpose, corrosion-resistant or fire-retardant)
Color and surface finish, including any UV protection
Loads, spans or mechanical properties you need to meet
Whether an existing die can be used or a new die is required

Key terms

Roving: A bundle of continuous glass fibers. Rovings provide most of the lengthwise strength in a pultruded profile.
Mat: A sheet of randomly oriented or stitched fibers that adds transverse strength.
Surface veil: A thin fiber layer at the surface that creates a resin-rich finish for corrosion and UV resistance.
Die: The heated steel tool that shapes and cures the profile.
Line speed: How fast the profile is pulled through the die. It is balanced against die temperature to achieve full cure.

FAQ

Why is it called pultrusion?

Because the material is pulled through the die, unlike extrusion, where material is pushed.

Can pultrusion make curved profiles?

Standard pultrusion makes straight, constant-section profiles. Curved shapes need specialized processes or other methods.

What is the minimum order for a custom die?

It depends on the profile and die cost. Contact us with the drawing and expected annual quantity.

Are pultruded profiles stronger than molded products?

Along their length, pultruded profiles have higher strength and stiffness because most fibers run in that direction. Molded products are more balanced.

Which resin is used in pultrusion?

Polyester and vinyl ester are most common. Other systems are used for special requirements.

How long can a pultruded profile be?

Pultrusion is continuous, so length is mainly limited by transport and handling. Profiles are cut to the length you order.

Related guides

Sources

ACMA, composites industry and processes overview: https://acmanet.org/composites-industry/
BSI, EN 13706 "Specifications for pultruded profiles": https://knowledge.bsigroup.com/products/reinforced-plastics-composites-specifications-for-pultruded-profiles-specific-requirements
A US FRP grating manufacturer, "Molded vs. Pultruded Fiberglass Grating" (fiber direction in pultruded products)