FRP & pultrusion glossary

Plain-language definitions of the materials, process, properties, products, and standards behind pultruded fiber reinforced polymer (FRP). Written for engineers, specifiers, and procurement professionals working with composites for the first time.

Materials & constituents

FRP (Fiber Reinforced Polymer)

A composite material made of a thermoset polymer resin matrix reinforced with high-strength fibers, most commonly E-glass. The fibers carry the mechanical load; the resin transfers load between fibers and protects them from the environment. FRP is the generic North American term and may use glass, carbon, aramid, or basalt reinforcement.

GRP / GFRP

(Glass) Fiber Reinforced Polymer or Plastic — the common UK, European, and Australian name for glass-fiber FRP. GRP and GFRP are interchangeable with 'fiberglass FRP'; the term specifies that the reinforcement is glass fiber.

Fiberglass

Informal term that refers either to the raw E-glass fiber reinforcement or to the finished glass-FRP composite. Strictly, fiberglass is the fiber and FRP is the finished composite — so a 'fiberglass I-beam' is a pultruded FRP I-beam reinforced with E-glass.

Resin matrix

The thermoset polymer that binds the reinforcement, transfers stress between fibers, and resists the service environment. Typical matrices are isophthalic polyester, vinyl ester, polyurethane, phenolic, and epoxy. Matrix choice sets chemical resistance, fire performance, and temperature limit.

E-glass roving

Continuous bundles of electrical-grade glass filaments aligned in the lengthwise direction of a pultruded profile. Roving is the dominant reinforcement by mass and carries the axial (longitudinal) load. ECR-glass is a corrosion-resistant variant.

Continuous strand mat (CSM)

A randomly oriented glass-fiber mat layered between roving to add transverse strength and through-thickness integrity, reducing the directional weakness of unidirectional roving alone.

Surfacing veil

A thin (0.2–0.4 mm) polyester or C-glass veil applied at the profile surface to create a resin-rich, UV-stable outer skin that protects the structural reinforcement from weathering and chemical attack.

Isophthalic polyester resin

The general-purpose structural matrix offering the best cost/performance balance. Heat deflection temperature roughly 90–100 °C. Suitable for most dry, mildly corrosive, and outdoor applications when paired with a UV-stable veil.

Vinyl ester resin

A matrix with superior resistance to acids, chlorides, hydrolysis, and osmotic blistering, specified for marine and aggressive chemical environments. Heat deflection temperature roughly 105–120 °C; typically adds 15–30% to profile cost.

Polyurethane (PU) resin

A tough, fast-curing matrix with 3–5× the flexural toughness of polyester, used where impact resistance matters — for example rail interiors and EV battery trays.

Phenolic resin

A fire-performance matrix achieving Class 1 surface spread of flame (BS 476 Part 7) with low smoke and low toxicity. Specified for offshore platforms, tunnels, and rail interiors governed by EN 45545-2.

Fiber content / fiber volume fraction

The proportion of reinforcement in the composite, usually quoted as glass content by weight (typically 60–70% for pultruded structural profiles). Higher fiber content raises strength and stiffness. Verified by burn-off testing per ASTM D2584.

Mechanical & physical properties

Tensile strength

The maximum lengthwise stress a profile withstands before failure — typically 240–400 MPa for E-glass/polyester pultrusions (comparable to A36 steel) at about one quarter of the weight. Measured per ASTM D638.

Flexural modulus (stiffness)

A measure of resistance to bending deflection — typically 12–20 GPa for pultruded FRP, roughly one tenth of steel's 200 GPa. Because modulus is low, deflection (not strength) usually governs FRP structural design. Measured per ASTM D790.

Interlaminar shear strength (ILSS)

The resistance to shear failure between the composite's layers, an indicator of fiber-resin bond quality — typically 20–30 MPa. Low ILSS shows up as delamination. Measured by the short-beam method, ASTM D2344.

Barcol hardness

A quick surface-hardness reading (typically 40–55 for pultruded FRP) used as a production check that the resin is fully cured. Measured per ASTM D2583.

Coefficient of thermal expansion (CTE)

How much the material expands per degree of temperature change — about 8 × 10⁻⁶ /°C lengthwise for pultruded FRP, close to glass and much lower than aluminum, which is why FRP window frames stay dimensionally stable.

Creep

Slow deformation under sustained load over time. Polyester-matrix FRP creeps under long-term high stress, so design codes apply a reduction factor (typically 0.25–0.35) to allowable stresses for permanent loads.

Dielectric strength

The voltage a material insulates before electrical breakdown — 10–14 kV/mm for FRP. Combined with its non-conductivity, this is why FRP is specified for substations, rail insulators, and RF-transparent structures.

HDT / glass transition temperature (Tg)

Temperature limits of the cured resin. Heat deflection temperature (HDT) marks where the matrix softens under load — about 90–100 °C for polyester, 105–120 °C for vinyl ester, 140–160 °C for phenolic. Service temperature should stay safely below these.

Fenestration

U-value (thermal transmittance)

The rate of heat loss through a window or frame, in W/m²·K — lower is better. F1 Composite FRP windows reach whole-window U-values down to 0.78 W/m²·K. Calculated per EN ISO 10077-1.

Thermal break

An insulating barrier inserted into a conductive frame (typically aluminum) to slow heat transfer. FRP frames need no thermal break because the composite already conducts heat at ~1/500 the rate of aluminum.

Passive House / PHI certification

A rigorous low-energy building standard from the Passive House Institute (PHI). F1 Composite's 90-series FRP window frame is PHI-certified, qualifying it for Passivhaus and ultra-low-energy buildings.

Keep exploring

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