Fibre Reinforced Facade Encyclopedia: Materials
Glass fibre reinforced polymer is the subset of fibre reinforced polymer in which the reinforcement is glass, almost always E glass or its corrosion resistant variant ECR glass, held in a cured thermoset resin. It is written glass fiber reinforced polymer in North America and sold as fibreglass in everyday use, and it accounts for the overwhelming majority of architectural composite laminates. The broader FRP page covers resins, processes and fire pathways; this page is about what the glass itself contributes and where its limits are.
An E glass filament is roughly 15 microns across and has a tensile strength of about 3,400 MPa, higher than most structural steel. A finished hand laid laminate reaches 150 to 250 MPa because only 20 to 30 percent of its volume is fibre, and the fibres point in every direction at once.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Fibre type | E glass standard; ECR glass for corrosion resistance | Alumino-borosilicate glass, low alkali content |
| Filament diameter | 9 to 24 microns | Bundled into strands, rovings and fabrics |
| Filament tensile strength | 3,100 to 3,400 MPa | Falls once handled, sized and wetted out |
| Fibre elastic modulus | 72 to 76 GPa | About one third of carbon fibre |
| Fibre density | 2,540 to 2,600 kg/m³ | Denser than resin, so fibre content raises laminate density |
| Fibre volume fraction | 20 to 30% hand lay-up; 40 to 60% infusion | The single largest driver of laminate properties |
| Laminate density | 1,600 to 1,900 kg/m³ | Glass and polyester or vinyl ester |
| Laminate flexural strength | 150 to 250 MPa | ShapeShell-RT published range 221 to 241 MPa |
| Laminate elastic modulus | 10 to 25 GPa | Low; facade panels are designed to deflection, not strength |
| Fire | Polymer matrix; reaction-to-fire classification only | Never non-combustible, whatever the fibre is |
E glass, ECR glass and where AR glass does not belong
E glass is an alumino-borosilicate formulated originally for electrical insulation, which is where the E comes from. Its defining feature for composites is a low alkali content of its own, typically under one percent, which keeps it electrically and chemically stable inside a resin. ECR glass is a boron free variant with better acid and corrosion resistance, used where the laminate is exposed to chemical attack or long term moisture. S glass and R glass raise stiffness and strength at a cost that architectural work almost never justifies.
The distinction that causes the most confusion on submissions is between E glass and alkali resistant glass. They are not interchangeable and they do not belong to the same material family. E glass belongs in a polymer matrix, where the surrounding resin is chemically neutral and the fibre is protected. Alkali resistant glass, with 16 percent or more zirconia, belongs in a cement matrix, where the pore solution sits at pH 12 to 13 and would attack E glass within a few years.
The fibre to resin interface
Glass and cured resin do not naturally bond well. Every commercial glass fibre is therefore coated at the bushing with a sizing, a thin chemical layer typically based on silane coupling agents, which forms a bridge between the silica surface and the polymer chain. The sizing is matched to the resin family, so a roving sized for polyester will not develop full strength in an epoxy laminate.
This interface, not the fibre and not the resin, is where most in service failures start. Poor wet-out leaves dry fibre and voids; voids admit water; water migrating along the interface causes interlaminar failure and, on a gel coated surface, osmotic blistering. It is the reason laminate quality control focuses on void content, resin to glass ratio and cure rather than on tested strength alone.
Fibre architecture
How the glass is arranged decides what the laminate can do. Chopped strand mat has short randomly oriented fibres and gives an isotropic laminate at low fibre volume, easy to conform to double curvature and the mainstay of moulded architectural work. Woven roving interlaces continuous bundles in two directions for much higher in-plane strength, at the cost of crimp where the bundles cross. Stitched biaxial and triaxial fabrics remove the crimp by holding straight fibres together with a light stitching thread. Unidirectional fabric places nearly all the fibre one way, which is how a rib or a stiffened edge is reinforced.
A real facade laminate is a schedule of these layers, not one material. A typical build is a gel coat, a fine surface tissue to keep fibre pattern off the face, chopped strand mat to develop thickness and conformability, and directional fabric where the panel needs to span. Because properties differ by direction and by layer, laminate design is done by schedule and checked by test panel, and fibre content is verified on production samples by ignition loss to ASTM D2584.
GFRP compared with carbon fibre reinforced polymer
Carbon fibre reinforced polymer replaces glass with carbon at roughly 230 GPa fibre modulus against 72 for E glass, and about 1,800 kg/m³ fibre density against 2,550. Where deflection governs, which is almost always the case on a facade panel, that stiffness is the whole argument for carbon, and a hybrid laminate with carbon only in the ribs is often the efficient answer.
Glass wins on everything else in architectural work. It costs an order of magnitude less per kilogram, it is electrically insulating and so raises no galvanic concern against aluminium or stainless steel supports, it is transparent to radio frequency, it tolerates the wide tolerances of moulded architectural production, and it is available in the mat and fabric forms that suit double curvature. Carbon appears in facades only where a deflection limit cannot be met any other way.
GFRP on facades
Architectural GFRP is laminated into single skin panels of 3 to 8 mm, monocoque shells of 10 to 50 mm overall depth, and sandwich constructions with a foam or honeycomb core. In service the panels run 5 to 32 kg per square metre, which is why GFRP is chosen for recladding, long unsupported spans, deeply modelled geometry and any element that has to be lifted without heavy plant.
The fire position is set by the matrix, not the glass. Glass fibre is inorganic and softens above 800 °C, but it is dispersed through a polymer that burns, so a GFRP laminate cannot pass a combustibility test under AS 1530.1, EN ISO 1182 or ASTM E136. It is classified instead by reaction-to-fire tests and, for external walls, by full-scale facade testing. ShapeShell-RT holds an AS 5637 Group 1 classification from AWTA Product Testing, an EN 13501-1 classification of B-s2, and a pass of the full-scale BS 8414 and AS 5113 test at BRE Global, which is the evidence a fire engineer uses to support a Performance Solution. It is not, and cannot be, non-combustible.
Standards and references
- ASTM D578 Standard Specification for Dimensions and Tolerances of Textile Glass Fibers; ISO 2078 (glass fibre yarns)
- ASTM D2584 (ignition loss, fibre content) and ASTM D2734 (void content)
- ASTM D790 and ISO 14125 (flexural); ASTM D638 and ISO 527 (tensile); ASTM D2344 (short beam interlaminar shear)
- EN 13501-1 (reaction to fire), AS 5637.1 (group number), AS 1530.3, ASTM E84
- AS 5113, BS 8414 with BR 135, NFPA 285 (full-scale facade tests)
- IBC Section 2612 / 2613, Fiber-reinforced polymer; ACI 440 for structural GFRP reinforcement
- ASTM C1666 (alkali resistant glass fibre), for contrast: the cementitious fibre standard, not applicable to GFRP
Related terms
Questions specifiers ask
Is GFRP the same as FRP?
GFRP is the glass reinforced subset of FRP. FRP is the parent category and also covers carbon, aramid and basalt reinforcement. In architecture the two terms are used almost interchangeably because nearly all architectural FRP is glass reinforced.
Can E glass be used in glass fibre reinforced concrete?
No. E glass has a low alkali content of its own but no resistance to the alkali in cement, and it loses most of its strength in a cement matrix within a few years. Cementitious composites require alkali resistant glass with 16 percent or more zirconia.
Why is GFRP used instead of carbon fibre on facades?
Cost, availability in mat and fabric forms suited to curved moulds, and the absence of any galvanic concern against metal supports. Carbon is specified only where a deflection limit cannot be met with glass, and is often used as a hybrid in ribs rather than across the whole panel.
Is GFRP non-combustible?
No. The reinforcement is inorganic but the matrix is a thermoset polymer, so the laminate cannot pass AS 1530.1, EN ISO 1182 or ASTM E136. GFRP is classified by reaction-to-fire tests and, for external walls, by full-scale tests such as AS 5113 or NFPA 285.
What fibre content should an architectural GFRP laminate have?
Typically 20 to 30 percent by volume for hand lay-up and 40 to 60 percent for vacuum infusion. It is verified on production samples by ignition loss to ASTM D2584 rather than taken from the specification.
Does GFRP degrade in sunlight?
The glass does not, but the resin surface does. Architectural laminates are protected by a gel coat or a PVDF paint system, and that surface treatment is part of the specification, not an optional finish.
Specifying a glass fibre reinforced polymer facade? ShapeShell-RT runs 5 to 32 kg per square metre with published flexural strength of 221 to 241 MPa and a full-scale AS 5113 pass at BRE Global. See ShapeShell-RT specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.