Fibre Reinforced Facade Encyclopedia: Properties
Strength to weight ratio is a material’s strength divided by its density, also called specific strength, and it is conveniently expressed in kilonewton metres per kilogram. It is the number behind every lightweight cladding argument: it explains why a 5 kg per square metre FRP panel and a 360 kg per square metre precast panel can be asked to do the same facade job, and why the structure under them is not remotely the same.
A square metre of 150 mm precast weighs about 360 kg. The same square metre of moulded GRC weighs 30 to 50 kg, and of FRP as little as 5 kg. On a twenty storey tower that difference is measured in tonnes per floor.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Architectural FRP laminate | 150 to 250 MPa flexural at 1.5 to 1.8 g/cm³ | roughly 90 to 160 kN·m/kg; ShapeShell-RT published at 221 to 241 MPa |
| Sprayed GRC | 20 to 30 MPa flexural at 1.9 to 2.1 g/cm³ | roughly 10 to 16 kN·m/kg |
| GRG, alpha gypsum | 24 MPa flexural at about 1.7 to 1.9 g/cm³ | ShapeShell-RG published at 24 MPa; interior use |
| Precast concrete | 4 to 6 MPa flexural at about 2.4 g/cm³ | roughly 2 kN·m/kg |
| Mild steel | 250 to 350 MPa yield at 7.85 g/cm³ | roughly 32 to 45 kN·m/kg |
| Aluminium 6063-T6 | 170 to 215 MPa yield at 2.70 g/cm³ | roughly 63 to 80 kN·m/kg |
| Panel weight, FRP | 5 to 32 kg/m² | ShapeShell-RT published range |
| Panel weight, GRC | 30 to 50 kg/m² | ShapeShell-RC published range |
| Panel weight, GRG | about 23 kg/m² | ShapeShell-RG, cast as a 3 to 6 mm shell |
How the ratio is calculated
Specific strength is strength divided by density. Working in megapascals and grams per cubic centimetre gives an answer in kilonewton metres per kilogram. The units matter less than the consistency, because a comparison is only valid when the same strength property is used for both materials: flexural against flexural, yield against yield. Setting the flexural strength of a composite against the yield strength of steel makes a composite look better than it is.
For facade panels the relevant strength is flexural, because wind load puts a thin panel into bending. Density comes from BS EN 1170-6 for a cementitious composite and ISO 1183 or ASTM D792 for a laminate.
Specific stiffness is usually the real constraint
Dividing elastic modulus by density gives specific stiffness, and that is the honest comparison for a facade panel, because deflection rather than strength normally sizes the element. On that measure the composites lose their advantage: steel and aluminium both sit near 26 MN·m/kg, while an FRP laminate at 7 to 15 GPa and a glass fibre reinforced concrete (GRC, GFRC) skin at 10 to 20 GPa sit well below them.
Composites win it back through geometry. A moulded panel is not a flat plate. Ribs, returns, folds and double curvature put material where the bending stress is, and the section modulus that results carries the load. The strength to weight argument for moulded FRP and GRC is really an argument about form.
What the ratio buys on a building
- Structure: a lighter facade reduces the permanent action the frame and footings carry, and the seismic mass that drives earthquake design
- Substructure: light panels hang from small brackets and light rails, so there are fewer and smaller penetrations through the insulation line
- Craneage: panels two people can handle change the lifting plan, the crane hire and the program
- Transport: a container of FRP panels carries far more facade area than a truck of precast
- Recladding: on an existing building the weight of the new facade is often the binding constraint
This is why weight per square metre, not specific strength, is the number that appears in a facade specification. Specific strength explains why the weight is achievable; dead load is what the structural engineer signs.
Where the ratio misleads
The ratio is also silent on stiffness, creep, impact damage, thermal movement, surface durability and cost. A material can be three times better on specific strength and still be wrong, because it deflects too far, moves too much at the joints, or cannot take the finish the architecture requires.
Choosing between them
In practice the choice is made on the constraints that bind: the fire requirement for the building type and height, the weight the structure can accept, the geometry, the finish and the exposure. Specific strength tells you what is possible at a given weight, not which material to use, and FRP compared with GRC sets out that comparison properly.
Standards and references
- AS/NZS 1170.1 Structural design actions, Permanent, imposed and other actions
- AS 1170.4 Structural design actions, Earthquake actions in Australia, where facade mass matters
- ISO 1183 and ASTM D792 Determination of the density of plastics and composites
- BS EN 1170-6 Test method for glass-fibre reinforced cement, Water absorption by immersion and dry density
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products
- AS 5637.1 and AS/NZS 1530.1, cited here only for the fire qualification noted above
Where this matters on a ShapeShift project
Spanda: A large sculptural form where the weight of each element, not its strength, set the fixing design, the lifting method and the supporting structure.
Related terms
Questions specifiers ask
What is a good strength to weight ratio for a facade panel?
There is no threshold. Architectural FRP sits around 90 to 160 kN·m/kg and sprayed GRC around 10 to 16, but the number that goes in a specification is weight per square metre.
Why is FRP so much lighter than GRC?
Higher specific strength lets the laminate be far thinner. A 3 mm FRP skin and a 15 mm GRC skin can carry comparable wind loads, and thickness times density is the panel weight.
Does lighter mean less durable?
Not in itself. Durability depends on the degradation mechanism and the exposure, not on mass. Both GRC and coated FRP are designed for a 40 to 50 year life under normal exposure.
Which is lighter overall, FRP or GRC?
FRP, at 5 to 32 kg per square metre against 30 to 50 for GRC. The choice between them is usually made on fire pathway, finish and geometry rather than on weight alone.
Weighing a facade option against the structure that has to carry it? ShapeShift supplies panel weights and fixing loads for GRC, FRP and GRG at concept stage. Open the facade calculators
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.