Fibre Reinforced Facade Encyclopedia: Materials
Fibreglass is the everyday name for glass fibre and for composites made from it, spelled fiberglass in North America. It is not a technical designation and it does not appear in material standards. Depending on who is using it, it means the glass filament itself, a glass fibre reinforced polymer laminate, or glass wool insulation, and those are three unrelated products with different densities, different uses and different fire behaviour. On a facade project the term that belongs in the specification is GFRP or FRP.
An architectural GFRP panel has a density around 1,700 kg per cubic metre and carries wind load. Glass wool insulation has a density of 10 to 100 kg per cubic metre and carries nothing. Both are called fibreglass in ordinary speech.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Meaning 1: the reinforcement | Glass filaments 9 to 24 microns across | Correctly called glass fibre |
| Meaning 2: the composite | Laminate 3 to 8 mm as a single skin | Correctly called GFRP, or FRP as the wider family |
| Meaning 3: the insulation | Glass wool batts at 10 to 100 kg/m³ | A different product with a different manufacture |
| GFRP laminate density | 1,600 to 1,900 kg/m³ | ShapeShell-RT single skin range |
| GFRP panel weight | 5 to 32 kg/m² | ShapeShell-RT published range |
| Flexural strength, laminate | 150 to 250 MPa | ShapeShell-RT: 221 to 241 MPa |
| Glass content, hand lay-up | 25 to 45% by weight | Verified by ignition loss on production samples |
| Service temperature | Governed by resin, typically 60 to 120 °C | The glass is unaffected at those temperatures |
| Fire | No inherent classification | ShapeShell-RT: AS 5637 Group 1, AWTA Product Testing |
The three things people mean
The first is the fibre. Drawn glass filaments, supplied as roving, chopped strand, mat or woven fabric, used to reinforce a polymer or a cement matrix. The glass fibre entry covers grades and properties.
The second is the composite, which is what an architect usually means by a fibreglass panel: glass fibre in a cured thermoset resin, moulded into a thin stiff shell. Engineers call this GFRP, glass fibre reinforced polymer, or FRP when the fibre might also be carbon or aramid.
The third is glass wool, the insulation product made by spinning molten glass into a low density mat. It shares a raw material with the other two and has nothing else in common with them. In North America fiberglass most often means this, which is a frequent source of confusion in international correspondence.
Why the trade term is imprecise
Written into a specification, fibreglass conveys almost nothing that can be checked on delivery. It does not state the resin family, and polyester, vinyl ester, epoxy and phenolic differ substantially in water resistance, toughness and fire behaviour. It does not state the glass content, which is the single strongest determinant of strength. It does not state the fibre architecture, and a random mat laminate and a stitched biaxial laminate of the same weight are not interchangeable. It does not state the laminate schedule, the thickness, the cure regime or the surface system.
Most importantly it says nothing about fire. There is no such thing as a fire rating for fibreglass as a category. Reaction to fire is a property of a tested laminate, with a named standard, a named testing body and a report number, and any claim made without those three things should be rejected on sight.
How the terms map
- Fibreglass, the fibre: glass fibre, with a grade such as E glass, ECR glass or AR glass
- Fibreglass, the laminate: GFRP (glass fibre reinforced polymer), a subset of FRP
- Fibreglass reinforced plastic, FRP, GRP: the same laminate, different regional habits
- Fibreglass insulation: glass wool or mineral wool, a thermal and acoustic product
- Fibreglass in concrete: almost always AR glass fibre, and the resulting material is GRC or GFRC, not fibreglass
The last line causes real trouble. Ordinary E glass fibreglass in a cement matrix loses most of its strength within a few years because the alkali in the cement attacks the glass. Glass fibre reinforced concrete uses alkali resistant glass with at least 16 percent zirconia, and the substitution is not visible on delivery.
Where fibreglass is used in building
Moulded facade panels and rainscreen skins, sunshades, fins and soffits, column and column head casings, dome and vault linings, sculptural and public art elements, cooling tower and plant room components, pultruded gratings, handrails and structural sections, water and chemical tanks, and pool shells. The common thread is complex geometry produced cheaply from a mould, high strength for very low weight, and no corrosion.
Its limits are equally consistent: a comparatively low elastic modulus, so deflection rather than strength usually governs a panel; a service temperature set by the resin; thermal movement roughly twice that of concrete, which makes joint design important; and an organic matrix that must be dealt with explicitly wherever external wall fire provisions apply.
What to write instead
Specify the material as glass fibre reinforced polymer, then state the resin family, the minimum glass content by weight, the laminate schedule or the minimum thickness, the surface system, the design wind pressure and deflection limit, and the fire evidence with standard, testing body and report reference. Reference the FRP and GFRP entries for the property data, and the specification entry for the structure of the clause.
Standards and references
- ASTM D578 Standard Specification for Glass Fiber Strands
- ISO 1172 and ASTM D2584 (glass content by ignition loss)
- ASTM D790 and ISO 14125 (flexural properties of composites)
- AS 5637.1 group number and AS 1530.3 early fire hazard
- EN 13501-1 reaction to fire classification; ASTM E84 surface burning characteristics
- AS 5113 and BS 8414 with BR 135 (full scale facade fire tests)
Related terms
Questions specifiers ask
Is fibreglass the same as FRP?
Not quite. Fibreglass is the colloquial name; FRP, fibre reinforced polymer, is the technical term for the composite, and GFRP names it specifically when the fibre is glass. FRP also covers carbon and aramid reinforced composites, which fibreglass does not.
Is fibreglass the same as fiberglass?
Yes. Fibreglass is the Australian and British spelling and fiberglass the North American one. In North America the word more often refers to glass wool insulation than to a moulded composite panel.
Is fibreglass fire rated?
Not as a category. A specific laminate can be tested and classified, for example to AS 5637.1 for a group number or to EN 13501-1. Any claim must name the standard, the testing body and the tested build-up. Fibreglass is never non-combustible, because the resin matrix is organic.
Can fibreglass be used to reinforce concrete?
Only alkali resistant glass fibre can. Ordinary E glass fibreglass is attacked by the alkalinity of cement and loses most of its strength within a few years. The correct material is glass fibre reinforced concrete made with AR glass.
How strong is fibreglass?
A hand laid architectural laminate typically reaches 150 to 250 MPa in flexure at a density around 1,700 kg per cubic metre, which is a very high strength to weight ratio. Stiffness is modest, around 10 to 25 GPa, so deflection usually governs panel design.
Specifying a moulded composite facade and want the correct terminology, laminate schedule and test evidence in one place? Start with the ShapeShell-RT data sheet. See ShapeShell-RT specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.