75% lighter than steel
Density 1.8–2.1 g/cm³ vs 7.85 g/cm³ for steel. Enables manual handling, smaller cranes, and lower freight cost.
FRP Guide
What is FRP? A complete guide to fiberglass reinforced polymer composites
FRP — fiber reinforced polymer, also known as fiberglass reinforced polymer or GRP — is a structural composite made of glass fiber reinforcement and a polymer resin matrix. This guide explains the materials, the pultrusion process, properties, standards, and how advanced FRP composites compare with steel and aluminum.
Definition
What is FRP?
FRP (fiber reinforced polymer) is a structural composite material that combines two constituents: a thermoset polymer resin matrix (polyester, vinyl ester, polyurethane, phenolic, or epoxy) and a high-performance fiber reinforcement (typically E-glass, also called fiberglass). The fibers carry the mechanical load; the resin transfers the load between fibers and protects them from the environment.
The resulting fiberglass reinforced polymer is lighter than aluminum, stronger per kilogram than steel, immune to rust, electrically non-conductive, and thermally insulating. FRP composites are used wherever corrosion, weight, electromagnetic transparency, or thermal efficiency is critical — from chemical plant platforms and offshore grating to passive-house window systems and pedestrian bridges.
When the FRP is produced by the pultrusion process, it is called pultruded FRP. The full F1 Composite pultruded product range is documented on the pultruded FRP profiles hub.
Terminology
FRP, GRP, fiberglass, composites — same thing?
The terminology around fiber composites is regional and often overlapping. In engineering practice:
- FRP — Fiber Reinforced Polymer. The generic North American term. Can use glass, carbon, aramid, or basalt fibers.
- GRP / GFRP — (Glass) Fiber Reinforced Polymer / Plastic. Common in the UK, EU, and Australia. Specifies glass-fiber reinforcement.
- Fiberglass — Informal North American term. Refers either to the raw E-glass fiber or to the finished glass-FRP composite.
- Composites — Umbrella term for any material combining two or more constituents. In structural use, usually means continuous-fiber FRP.
- Advanced composites — Composites with engineered fiber architectures and controlled fiber fractions (≥ 50% by weight). Pultruded FRP profiles qualify.
- Pultruded composites / pultruded profiles — FRP composites manufactured by the pultrusion process — the focus of F1 Composite.
Composition
What is inside a pultruded FRP profile?
Reinforcement (60–70% by weight)
- E-glass roving — unidirectional fiber bundles carrying axial load. The dominant reinforcement by mass.
- Continuous strand mat (CSM) — randomly oriented glass mat that adds transverse strength and through-thickness integrity.
- Woven roving / biaxial fabric — used in custom profiles requiring balanced in-plane stiffness.
- Surfacing veil — polyester or C-glass veil that gives a resin-rich, UV-stable outer surface. Typically 0.2–0.4 mm thick.
- ECR-glass / carbon / basalt / aramid — optional reinforcements for enhanced corrosion resistance, high modulus, or specialty requirements.
Polymer matrix (30–40% by weight)
- Isophthalic polyester — general structural use. Best cost / performance balance.
- Vinyl ester — superior chemical, chloride, and hydrolysis resistance. Preferred for marine and chemical environments.
- Polyurethane (PU) — 3–5× the flexural toughness of polyester; fast cure; used in rail interiors and EV battery trays.
- Phenolic — Class 1 fire performance (BS 476 / EN 45545-2). Low smoke, low toxicity.
- Epoxy — highest mechanical properties; specified when tensile or fatigue requirements approach steel equivalents.
- Additives — UV stabilizers, flame retardants, pigments, release agents, and catalysts (MEKP for polyester; BPO for vinyl ester).
Manufacturing
How pultruded FRP is made
Pultrusion is a continuous, automated process that produces constant-cross-section FRP profiles. Invented in the 1950s and standardized in the 1970s, it is now the dominant manufacturing route for structural FRP shapes worldwide.
1. Creel
Thousands of E-glass roving packages are fed from a creel frame, aligned in the longitudinal direction.
2. Resin impregnation
Fibers are pulled through an open resin bath or closed injection chamber, fully wetted with liquid thermoset resin.
3. Pre-former
Impregnated fibers pass through guide plates that compact the material into the required cross-section geometry.
4. Heated die
The compacted fiber/resin bundle enters a heated steel die (typically 120–180 °C) where the resin cures.
5. Pullers
Reciprocating or caterpillar pullers draw the cured profile at 0.3–1.5 m/min, providing the continuous 'pulling' action that names the process.
6. Cut-off
A synchronized flying saw cuts profiles to length — typically 6 m or 12 m for shipping — and they are stacked for inspection.
Custom die lead time
Creating a new custom profile typically takes 6–10 weeks total:
- Cross-section design & approval1–2 weeks
- Steel die manufacturing3–6 weeks
- Trial run & sample approval1 week
- First production batch1–2 weeks
Properties
Mechanical and physical properties of pultruded FRP
Typical values for E-glass / isophthalic-polyester pultruded structural profiles at 23 °C. Properties are directional — the table below gives longitudinal (L) values unless noted. Vinyl ester and polyurethane systems provide 10–25% higher strength.
| Property | Value | Test standard |
|---|---|---|
| Density | 1.8 – 2.1 g/cm³ | — |
| Tensile strength (L) | 240 – 400 MPa | ASTM D638 |
| Tensile modulus (L) | 17 – 28 GPa | ASTM D638 |
| Flexural strength (L) | 200 – 350 MPa | ASTM D790 |
| Flexural modulus (L) | 12 – 20 GPa | ASTM D790 |
| Compressive strength (L) | 200 – 300 MPa | ASTM D695 |
| Interlaminar shear strength | 20 – 30 MPa | ASTM D2344 |
| Barcol hardness | 40 – 55 | ASTM D2583 |
| Coefficient of thermal expansion (L) | 8 × 10⁻⁶ / °C | ASTM E831 |
| Thermal conductivity | 0.3 W/m·K | ASTM C177 |
| Dielectric strength | 10 – 14 kV/mm | ASTM D149 |
| Water absorption (24 h) | < 0.6% | ASTM D570 |
| Glass fiber content by weight | 60 – 70% | ASTM D2584 (burn-off) |
| Dimensional tolerance | ±0.25 mm typical | EN 13706 / ASTM D3917 |
Advantages
Why engineers specify FRP over steel and aluminum
Corrosion-immune
No rust, no galvanic corrosion, no chloride pitting. Ideal for marine, chemical, and de-icing-salt environments.
Electrically non-conductive
Dielectric strength 10–14 kV/mm. Used for electrical substations, rail insulators, and RF-transparent structures.
Thermally insulating
Conductivity 0.3 W/m·K — about 1/170 of steel and 1/530 of aluminum. Enables passive-house-grade window systems.
Low maintenance
50–100 year design life with no painting, galvanizing, or recoating cycles. Zero-maintenance TCO advantage over 30 years.
Easy fabrication
Cut with carbide blade, drill with diamond bit, connect with stainless bolts or adhesive. No hot work permits, no welding.
Limitations
When FRP is not the right choice
FRP is not a universal substitute for steel. Engineering considerations that frequently disqualify or complicate a pultruded FRP specification:
- Low elastic modulus. FRP stiffness is ~1/10 of steel. For long-span primary beams, deflection often governs. Hybrid FRP–concrete or FRP–steel designs can be the right answer for spans beyond 10–12 m.
- Creep under sustained load.Polyester-matrix FRP creeps under long-term high stress; design allowables typically apply a 0.25–0.35 reduction factor for permanent loads.
- No welding. Thermoset FRP cannot be welded, heated, or bent after manufacture. All connections are bolted or adhesive bonded.
- Temperature limits. Isophthalic polyester has a heat deflection temperature (HDT) of 90–100 °C. Vinyl ester 105–120 °C. Phenolic 140–160 °C. For higher service temperatures, specialty resins or alternative materials are needed.
- Upfront cost. Per meter, FRP is 50–100% more expensive than carbon steel. Lifecycle economics favour FRP in corrosive environments, but marginal-environment projects may not justify the premium.
- UV degradation of resin-starved surfaces. Always specify a surfacing veil and a pigmented or UV-stabilized resin for outdoor service. Properly specified FRP shows less than 5% property loss after 20 years of direct UV exposure.
Standards
FRP composites — key standards and certification
| Standard | Scope |
|---|---|
| ISO 9001:2015 | Quality management system. F1 Composite certified. |
| EN 13706-1/2/3 | European pultruded profile standard. Defines structural grades E17 and E23, test methods, and classification. |
| ASTM D3917 | Standard specification for dimensional tolerance of thermosetting glass-reinforced plastic pultruded shapes. |
| ASTM D638 / D790 / D695 / D2344 | Test methods for tensile, flexural, compressive, and interlaminar shear properties. |
| ASCE/SEI 74-23 | Pre-Standard for LRFD Design of Pultruded FRP Structures (United States). |
| EUROCOMP Design Code | Structural design of polymer composites (Europe). |
| ASTM E84 / BS 476 | Fire: surface burning characteristics and fire tests on building materials. |
| EN 45545-2 | Fire: railway rolling stock — fire protection. |
| AS 4586 | Slip resistance classification for pedestrian surface materials (gratings). |
| PHI (Passive House Institute) | Thermal performance certification for fenestration systems. |
| DNV / Lloyd's Register | Marine certification for offshore structural FRP. |
Applications
Where advanced FRP composites are specified
Infrastructure & transport
- → Pedestrian bridges and bridge deck panels
- → Rail platform canopies and sub-structures
- → Cable trays and pipe supports for utility corridors
- → Highway noise barriers in corrosive environments
Energy & utilities
- → Transmission cross-arms and substation equipment
- → Solar mounting frames (utility-scale and rooftop)
- → Wind-turbine secondary structures
- → Oil & gas access platforms and ladders
Chemical & marine
- → Chemical plant walkways and handrails
- → Cooling tower structural elements
- → Wastewater and desalination plant gratings
- → Offshore platforms and floating docks
Building & construction
- → FRP window frames & FRP window profiles (passive-house, low-energy buildings)
- → Façade support profiles and curtain-wall mullions
- → Building rooftop platforms and antenna masts
- → Rebar for reinforced concrete in corrosive service
For a deeper overview by industry, see the industries section. For live case studies including before/after weight, cost, and delivered lead-time data, see our case studies.
FRP FAQ
FRP composites — frequently asked questions
Quick reference answers for engineers, specifiers, and procurement professionals new to advanced FRP composites.
What does FRP stand for?
FRP stands for Fiber Reinforced Polymer (sometimes written Fibre Reinforced Plastic). It refers to a composite material made of a polymer matrix — typically polyester, vinyl ester, polyurethane, epoxy, or phenolic resin — reinforced with high-strength fibers, most commonly E-glass. FRP is also called GRP (Glass Reinforced Polymer) in British and European usage.
Is FRP the same as fiberglass?
Fiberglass is the reinforcement material (glass fiber) used inside FRP composites. Everyday use often treats 'fiberglass' and 'FRP' as synonymous, but strictly speaking fiberglass is the raw fiber and FRP is the finished composite that combines fiberglass with a polymer resin. A fiberglass I-beam is therefore a pultruded FRP I-beam made with E-glass reinforcement.
Are FRP composites considered advanced composites?
Yes. Pultruded FRP profiles are classified as advanced composites because they use engineered fiber architectures (unidirectional roving, continuous strand mat, woven fabric) and controlled fiber-volume fractions of 60–70%. Advanced composites are distinguished from short-fiber or filled plastics by their tailored directional properties and structural-grade mechanical performance.
Is FRP stronger than steel?
Pultruded FRP has tensile strength of 240–400 MPa, comparable to A36 structural steel (400 MPa), but at about one quarter of the weight. Per kilogram, FRP is significantly stronger than steel. However, the elastic modulus of FRP (17–28 GPa) is roughly 1/10 that of steel (200 GPa), so stiffness and deflection usually govern design rather than strength.
Does FRP rust or corrode?
No. FRP does not rust, pit, or suffer galvanic corrosion. The polymer matrix is inert to most acids, bases, salts, and chlorinated environments. Vinyl ester resin is specified for aggressive chemical or marine environments, and vinyl ester FRP shows negligible property degradation after 30+ years of service in saltwater splash zones.
Is FRP flammable?
Standard polyester FRP is self-extinguishing (UL 94 V-0). With fire-retardant additives or phenolic resin, pultruded FRP achieves Class 1 surface spread of flame (BS 476 Part 7), low smoke, and low toxicity, and is approved for offshore platforms, tunnels, and rail interiors under EN 45545-2. Composites for rail and passenger transport use phenolic or modified acrylic systems.
How long do FRP composites last?
Pultruded FRP structures have a design life of 50–100 years with negligible maintenance when specified correctly (UV-stable surface, appropriate resin). Real-world installations in chemical plants, bridges, and marine environments have demonstrated 30+ years of service without measurable loss of mechanical properties.
Can FRP be recycled?
Thermoset FRP cannot be melted and re-formed like metals. Current end-of-life options include mechanical grinding to filler for cement or concrete (widely commercial), co-processing in cement kilns (energy recovery plus calcium oxide input), and emerging solvolysis/pyrolysis fiber-recovery routes. Non-hazardous landfill is permitted — FRP contains no heavy metals or toxic leachates.
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