FRP vs steel, aluminum, timber and concrete

Pultruded FRP has a density of 1.8–2.1 g/cm³, approximately one quarter that of steel (7.85 g/cm³) and roughly 70% of aluminum (2.70 g/cm³). Because FRP is less stiff, a replacement section is often deeper than the steel one, so the weight saving on a member is smaller than the density ratio suggests, but it usually remains large.

This weight reduction cascades: lighter members require smaller foundations, lower-capacity cranes (or no crane at all; many FRP profiles can be carried by two workers), fewer transport loads, and less energy during installation. For bridge decks, building facades, and offshore platforms, weight savings translate directly into cost savings and expanded design possibilities.

The tensile strength of pultruded E-glass FRP ranges from 350 to 700 MPa in the longitudinal (fiber) direction, which overlaps with and often exceeds the yield strength of structural steel (250–350 MPa). Carbon fiber reinforcement pushes tensile strengths above 1,000 MPa.

The key distinction is directionality: pultrusion produces primarily unidirectional reinforcement, so transverse strength is lower (50–100 MPa). For multi-directional loads, we incorporate continuous filament mat and multi-axial fabrics. We optimize fiber architecture for each application.

The elastic modulus of E-glass FRP is 20–40 GPa, roughly one fifth to one tenth that of steel (200 GPa). For a given cross-section, an FRP member deflects more than steel under the same load.

In deflection-governed designs, this is addressed by increasing the moment of inertia (deeper profiles, wider flanges, or hollow box shapes) or by using carbon fiber (100–150 GPa modulus). Because FRP is so much lighter, dead-load deflection is significantly lower, partially offsetting the modulus difference in real-world designs.

Corrosion resistance is the most compelling advantage of FRP over metals. Carbon steel rusts in humid air, accelerates in salt spray, and suffers severe degradation in chemical environments, requiring continuous expenditure on coatings, cathodic protection, and periodic replacement.

FRP is inherently immune to electrochemical corrosion because it contains no metal. Vinyl ester and epoxy resin systems resist a wide range of acids, alkalis, solvents, and salt solutions at elevated temperatures. In chemical plants, wastewater facilities, marine structures and coastal buildings, FRP profiles need no corrosion protection. Where the resin is matched to the exposure and the surface is protected from UV, the recoating avoided often offsets the higher initial cost.

FRP has a thermal conductivity of 0.3–0.5 W/m·K, roughly 100× lower than steel and about 500× lower than aluminum. This makes FRP an inherent thermal break.

In fenestration, FRP frames remove most of the thermal bridging that makes metal-framed openings the weak point of an envelope; how much energy that saves depends on the glazing, spacer and installation, so compare whole-window Uw values. In cold stores, LNG facilities and cryogenic environments, FRP reduces the condensation and ice formation that affect steel structures.

Glass-fiber FRP is an electrical insulator with a dielectric strength of 12–20 kV/mm, making it intrinsically non-conductive. This is critical for electrical utility applications (crossarms, switchgear enclosures), railway electrification, and worker safety.

Glass-fiber FRP is also non-magnetic, which matters for MRI room construction, EMC enclosures and radar-transparent applications. No metal combines this with electrical insulation.

Steel structures in corrosive environments require full repainting every 8–15 years at USD 30–60 per m² per cycle. Over 50 years, a steel structure may be repainted 3–5 times, adding 60–100% to the initial material cost. Timber requires resealing every 3–5 years and is subject to insect damage, rot, and fire.

FRP profiles need no corrosion painting, cathodic protection or preservative treatment. Surface care is limited to UV protection where the exposure calls for it, and inspection is the same as for any structure. When the full lifecycle cost is calculated, including installation, maintenance, downtime and disposal, FRP often has the lowest total cost in corrosive, marine and high-maintenance environments.

Embodied carbon of pultruded FRP (3.1–5.0 kg CO₂/kg) is higher than steel (1.8–2.5 kg CO₂/kg) per kilogram. However, because an FRP member is usually much lighter than the steel member it replaces, the CO₂ per functional unit (per meter of railing, per m² of grating) is often comparable to or lower than steel.

When avoided emissions from eliminated maintenance cycles and reduced transport energy are included in a full LCA, FRP frequently achieves a net carbon advantage over the service period. Aluminum carries the highest embodied carbon at 8–12 kg CO₂/kg, reflecting the energy of smelting.