GRP Standards: Pultruded Profiles
Guide To GRP Profiles Standards & Compliance
GRP pultruded profiles are one of the most versatile structural materials available to the UK construction, rail, water, marine, and utilities sectors. They are lighter than steel, do not corrode, require virtually no maintenance, are non-conductive, and deliver service lives measured in decades. But here is the problem: not all profiles are manufactured to the same standard, and the difference between a compliant product and a non-compliant one is invisible to the naked eye. You cannot tell by looking at a profile whether it meets EN 13706 E23 grade, whether the glass fibre content is 60% or 35%, whether the resin is fire-retardant isophthalic polyester or a cheap orthophthalic mix, or whether the dimensional tolerances are within specification. The only way to know is through documentation, test certificates, and traceability. This guide explains exactly what to look for, what to ask, and what should make you walk away.Understanding the Product: What Is a Pultruded GRP Profile?
Pultrusion is a continuous automated manufacturing process. The name combines ‘pull’ and ‘extrusion’ — continuous glass fibre reinforcements are pulled through a resin impregnation bath, then through a heated steel die where the resin cures, producing a rigid composite profile with a constant cross-section.
This is fundamentally different from hand lay-up, which is a manual process producing lower-strength products with different material properties. The two processes should never be confused or specified interchangeably, yet we regularly see specifications that conflate them.
Key characteristics of a properly pultruded profile:
- Glass fibre content: 60–70% by weight for structural profiles. This is what gives the product its strength. Anything below 50% should raise serious questions.
- Resin system: Isophthalic polyester is the standard for structural applications. It provides superior chemical and water resistance compared to cheaper orthophthalic resins. Vinyl ester is specified for aggressive chemical environments.
- Reinforcement: Continuous E-glass fibre rovings for longitudinal strength, combined with continuous filament mat (CFM) for transverse properties and woven roving fabric where additional strength is required.
- Surface finish: Polyester surface veil on all external surfaces, providing UV protection, improved chemical resistance, and a consistent finish.
- Constant cross-section: No joints, splices, or discontinuities within each length. Standard production runs yield 6m lengths or longer.
The Standard: EN 13706 Explained
The standard has three parts:
- EN 13706-1: Designation: establishes how profiles are classified and designated, including profile type, resin system, reinforcement type, and grade. A proper designation reads: ‘Pultruded I-beam 152×76×6.4 to BS EN 13706 Grade E23, isophthalic polyester, fire retardant, RAL 7035 grey.’
- EN 13706-2: Methods of test and general requirements: specifies all test methods for determining mechanical properties, dimensional tolerances, and quality assurance parameters. This is where the detail lives.
- EN 13706-3: Specific requirements: defines the minimum mechanical property requirements for two structural grades: E23 and E17.
Understanding the Grades: E23 vs E17
The grade number refers to the minimum full-section flexural modulus in gigapascals. E23 requires a minimum of 23 GPa; E17 requires 17 GPa. The higher the number, the stiffer and stronger the profile.
| Property | E23 | E17 | Test Method |
| Full section flexural modulus (GPa) | 23 | 17 | Annex D, EN 13706-2 |
| Tensile modulus — axial (GPa) | 23 | 17 | EN ISO 527-4 |
| Tensile modulus — transverse (GPa) | 7 | 5 | EN ISO 527-4 |
| Tensile strength — axial (MPa) | 240 | 170 | EN ISO 527-4 |
| Tensile strength — transverse (MPa) | 50 | 30 | EN ISO 527-4 |
| Pin-bearing strength — axial (MPa) | 150 | 90 | Annex E, EN 13706-2 |
| Pin-bearing strength — transverse (MPa) | 70 | 50 | Annex E, EN 13706-2 |
| Flexural strength — axial (MPa) | 240 | 170 | EN ISO 14125 |
| Flexural strength — transverse (MPa) | 100 | 70 | EN ISO 14125 |
| Interlaminar shear strength — axial (MPa) | 25 | 15 | EN ISO 14130 |
3. Dimensional Tolerances: The Hidden Quality Indicator
EN 13706-2 Annex B defines the dimensional tolerances that all pultruded profiles must meet. These are not optional — they are fundamental to ensuring that profiles fit together, perform structurally as designed, and are interchangeable.
For a typical profile such as a 50mm outside diameter tube with a 5mm wall thickness, the tolerances under EN 13706-2 are:
| Dimension | Tolerance | Acceptable Range |
| Outside diameter (50mm) | ±0.5mm | 49.5mm to 50.5mm |
| Wall thickness (5mm) | ±0.4mm | 4.6mm to 5.4mm |
| Straightness (bow) | Max 1.5mm per metre | — |
| Twist/angularity | ±2° | — |
| Cut length (up to 6m) | ±3mm | — |
Why does this matter? Because profiles that are out of tolerance do not fit connectors correctly, do not distribute loads as designed, and can create stress concentrations that lead to premature failure. You cannot see a 0.8mm wall thickness deviation, but it represents a 16% reduction in material — and potentially a proportionate reduction in structural capacity.
Ask your supplier: Are dimensional tolerances verified to EN 13706-2 Annex B? Can you provide dimensional inspection data?
4. Fire Classification: The Standard Has Changed
As of March 2025, BS 476-7 has been withdrawn from Approved Document B. The current mandatory standard for fire classification of construction products in the UK is EN 13501-1.
This is not a minor administrative change. EN 13501-1 is a fundamentally more rigorous standard. Where BS 476-7 tested only surface spread of flame, EN 13501-1 assesses ignitability, heat release rate, smoke production, and flaming droplets through multiple test methods including the Single Burning Item (SBI) test.
Critical point: Products tested under BS 476-7 cannot carry over their classification. They must be retested to EN 13501-1. Any supplier still quoting BS 476-7 classifications for new applications is quoting a withdrawn standard.
Understanding the EN 13501-1 Classification
The classification has three components:
| Component | What It Measures | Classes |
| Main class | Contribution to fire growth | A1, A2, B, C, D, E, F |
| Smoke (s) | Rate and total quantity of smoke produced | s1, s2, s3 |
| Droplets (d) | Production of flaming droplets or particles | d0, d1, d2 |
A classification of B-s1, d0 means: very limited contribution to fire (B), little or no smoke (s1), and no flaming droplets (d0). This represents the highest practical fire classification for a GRP product.
A classification of D-s2, d2 means: acceptable contribution to fire (D), moderate smoke (s2), and flaming droplets present (d2). This is a significantly lower performance.
Both are ‘compliant’ in the sense that they have been tested. The difference in real-world safety performance is enormous. Know what you are specifying.
5. Resin Systems: The Invisible Difference
The resin system is the matrix that binds the glass fibres together and determines the profile’s chemical resistance, water absorption, fire performance, and long-term durability. You cannot tell which resin system has been used by looking at a finished profile. This makes it one of the easiest corners to cut — and one of the most dangerous.
| Resin Type | Characteristics | Typical Use | Cost Indicator |
| Isophthalic polyester | Superior chemical and water resistance, good all-round performance | Standard structural profiles, most UK applications | Standard |
| Orthophthalic polyester | Lower chemical resistance, higher water absorption | Non-structural, low-cost applications only | 15–20% cheaper |
| Vinyl ester | Excellent chemical resistance, higher elongation | Aggressive chemical environments, marine | 20–30% more |
| Phenolic | Superior fire performance, low smoke and toxicity | Rail, tunnel, high fire-risk environments | 30–50% more |
The UK structural market standard is isophthalic polyester. If a supplier’s material data sheet says ‘polyester resin’ without specifying the type, press them. If they cannot confirm isophthalic, assume orthophthalic and price accordingly — both in cost and in risk.
Ask your supplier: What specific resin system is used? Is it isophthalic polyester? Can you provide the material data sheet specifying the resin type?
6. Quality Assurance and Traceability
EN 13706-2 defines quality assurance parameters that manufacturers must meet. ISO 9001 certification provides the management framework for consistent quality. Together, they form the minimum baseline for a credible supplier.
What a compliant supplier should be able to provide:
- Certificate of conformity confirming compliance with EN 13706 Parts 1, 2, and 3
- Specification of grade (E17 or E23) for each profile supplied
- Material data sheet detailing resin type, reinforcement type, and glass fibre content
- Fire classification certificate to EN 13501-1 with full classification (main class, smoke, droplets)
- Dimensional tolerance data to EN 13706-2 Annex B
- ISO 9001 quality management certification
- Batch traceability — the ability to trace any profile back to its production run, resin batch, and fibre lot
7. Surface Finish and Industrial Reality
GRP pultruded profiles are construction products with an industrial finish. They are not powder-coated consumer goods. It is important that buyers, quality inspectors, and end users understand what is normal and acceptable in a pultruded profile.
Normal characteristics of pultruded profiles:
- Minor surface marks: Small marks from the pulling process are inherent to pultrusion and do not affect performance.
- White streaks: Glass fibres occasionally show through the surface resin during production. This is a cosmetic feature, not a defect.
- Slight colour variation: Colour consistency between batches can vary slightly. This is normal for pigmented resin systems.
What is NOT acceptable:
- Visible cracks: Any cracking in the profile wall is a reject.
- Delamination: Separation of layers indicates a manufacturing defect.
- Significant dimensional deviation: Outside the tolerances specified in EN 13706-2 Annex B.
- Dry fibres: Exposed, un-wetted glass fibres indicate inadequate resin impregnation.
- Surface wear exceeding 10% of wall thickness: On used profiles, this indicates the product should be replaced.
8. Standard Colours and Bespoke Options
Most UK manufacturers stock profiles in two standard colours: Grey (RAL 7001) and Yellow (RAL 1004). Bespoke colours are available but typically require a minimum order quantity of 500 metres due to the resin pigmentation process.
The colour is integral to the resin — it is not a surface coating. This means it cannot chip, flake, or peel, and does not require repainting. However, prolonged UV exposure will cause some fading over time, which is why all quality profiles incorporate UV stabilisers in the resin formulation and polyester surface veil on external faces.
Ask your supplier: Does the profile include UV stabilisers in the resin? Is there a polyester surface veil on all external surfaces? These are not optional extras — they are fundamental to long-term performance.
9. Pultruded vs Moulded: Know the Difference
In the GRP market, both pultruded and moulded products are sold. They serve different purposes and are not interchangeable. Buyers must understand the difference.
| Characteristic | Pultruded | Moulded |
| Glass content | 60–70% by weight | 30–40% by weight |
| Strength direction | Unidirectional — very strong longitudinally | Bi-directional — equal in both directions |
| Flexural strength | ~207 MPa | ~172 MPa |
| Stiffness | 2x stiffer than moulded | More flexible, impact-resistant |
| Best for | Longer spans, heavier loads, structural framing | Shorter spans, cutouts, bi-directional loading |
| Process | Automated, continuous | Manual/semi-auto, batch |
Pultruded profiles are approximately 20% stronger in flexural strength and twice as stiff as moulded equivalents. For structural applications, handrails, platforms, stairs, and framing — pultrusion is the correct choice. Moulded grating has its place for shorter-span flooring where bi-directional loading and impact resistance are priorities.
10. The Buyer’s Checklist: 15 Questions to Ask Before You Order
Print this page. Take it to every supplier meeting. If you get satisfactory, documented answers to all fifteen, you are buying from a credible source. If you get vague answers, deflections, or promises to ‘send it later’ — proceed with extreme caution.
| # | Question | Good Answer | Red Flag |
| 1 | Is the profile manufactured by the pultrusion process? | Yes, continuous | Vague / mixed |
| 2 | Does it comply with EN 13706? | Yes, certified | ‘Similar standard’ |
| 3 | What grade — E17 or E23? | Specific grade stated | ‘We don’t grade’ |
| 4 | What resin system is used? | Isophthalic polyester | ‘Polyester’ only |
| 5 | What is the glass fibre content? | 60–70% by weight | Below 50% or unknown |
| 6 | Is there a surface veil on all external faces? | Yes, polyester veil | No / not sure |
| 7 | Can you provide mechanical test data? | Certified test report | ‘It’s on the website’ |
| 8 | What is the fire classification to EN 13501-1? | Full class e.g. B-s1,d0 | BS 476-7 only |
| 9 | Can you provide the fire test certificate? | Accredited lab report | ‘We’re getting tested’ |
| 10 | Are dimensional tolerances to EN 13706-2 Annex B? | Yes, verified | ‘Standard tolerances’ |
| 11 | Is production ISO 9001 certified? | Current certificate | No / expired |
| 12 | Can you provide a certificate of conformity? | Yes, per delivery | ‘On request only’ |
| 13 | Is there batch traceability? | Full traceability | No system in place |
| 14 | What is the declared design life? | Stated with evidence | ‘Long lasting’ |
| 15 | Do you have an Environmental Product Declaration (EPD)? | Published EPD | No / in progress |
11. The Bottom Line: If They Don’t Have the Paperwork, Walk Away
A GRP pultruded profile is only as good as the evidence behind it. The material itself is outstanding — lighter than steel, stronger for its weight, non-corrosive, non-conductive, with service lives exceeding 50 years and a carbon footprint that beats steel when properly assessed.
But those benefits only exist when the product is manufactured correctly, tested to the current standards, and supplied with full documentation. Without that evidence, you are placing your trust in appearances alone. And appearances, in the world of composite materials, count for nothing.
At Engineered Composites, every profile we supply comes with full traceability, EN 13706 compliance certification, EN 13501-1 fire classification, and the backing of ISO 9001 quality management. We invest in independent laboratory testing because it is the right thing to do — for our customers, for the end users who rely on our products, and for the reputation of the GRP industry as a whole.
We are not the only good supplier in this market. But there are also products being sold that cannot answer the fifteen questions listed in this guide. Those products put people at risk, undermine confidence in GRP as a material, and damage the entire industry.
