Fibre Reinforced Facade Encyclopedia: Properties
Density is mass per unit volume, in kilograms per cubic metre. For a facade it is an intermediate number rather than the answer. What a structural engineer, a facade engineer and an installer all actually work with is weight per square metre of finished panel, which is density multiplied by the effective thickness of the panel including its ribs, frame and fixings. A material with a high density can still produce a very light facade if it can be made thin, which is precisely the argument for thin section composites over precast concrete.
Glass fibre reinforced concrete is only about fifteen percent less dense than normal concrete. It produces a facade about a tenth of the weight, because it is cast at 15 mm instead of 150 mm.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Glass fibre reinforced concrete | 1,900 to 2,100 kg/m³ | Sprayed material at 28 days; typical |
| Glass fibre reinforced polymer (GFRP) | 1,700 to 1,900 kg/m³ | Glass fibre in a thermoset matrix; typical |
| Glass fibre reinforced gypsum | 1,400 to 1,700 kg/m³ | Alpha gypsum composites; typical |
| Normal weight concrete | 2,300 to 2,500 kg/m³ | For comparison; typical |
| Aluminium | about 2,700 kg/m³ | For comparison |
| ShapeShell-RC panel weight | 30 to 50 kg/m² | Published range for the ShapeShift GRC system |
| ShapeShell-RT panel weight | 5 to 32 kg/m² | Published range for the ShapeShift FRP system |
| ShapeShell-RG panel weight | about 23 kg/m² | Published figure; interior GRG cast as a 3 to 6 mm shell |
| 150 mm precast panel | about 360 kg/m² | For comparison; typical |
| Test methods | BS EN 1170-6, ASTM C948, ISO 1183 | Bulk density and water absorption on coupons |
Density versus weight per square metre
The two are routinely confused and the distinction decides facade design. Density describes the material in a laboratory. Weight per square metre describes the panel on the building, and it includes the skin, the ribs formed in the same pour, any stud frame, the anchors and any backing.
Glass fibre reinforced concrete (GRC, GFRC) at 1,900 to 2,100 kg per cubic metre is only marginally lighter as a material than the 2,300 to 2,500 of normal weight concrete. As a facade it is dramatically lighter, because it has no steel reinforcement to cover and can therefore be cast at 10 to 20 mm rather than 100 to 150 mm. ShapeShell-RC is published at 30 to 50 kg per square metre including ribs and frame, against roughly 360 kg per square metre for a 150 mm precast panel.
Fibre reinforced polymer goes further. It is a less dense material, around 1,700 to 1,900 kg per cubic metre, and it is laminated thinner again, so ShapeShell-RT is published at 5 to 32 kg per square metre. The spread in that range is mostly geometry and laminate schedule rather than material variation.
What panel weight decides
Weight per square metre propagates through the whole facade package and through the building behind it.
- Structural design: the dead load the slab edge, spandrel beam or backing wall has to carry, which on a tall building accumulates through every floor into the columns and the foundations
- Substructure: bracket and rail sizes, fixing capacity into the structure, and the number of fixings per panel
- Panel size: the maximum panel a crane can lift at reach, which usually controls panel format more than manufacturing does
- Craneage: crane class, lift radius, cycle time and therefore the cost and duration of installation
- Thermal bridging: fewer and smaller brackets through the insulation, which improves the effective U-value of the wall
- Seismic and dynamic response: mass at the perimeter of a building affects its dynamic behaviour
- Recladding feasibility: whether an existing structure can carry a new facade at all, which is often the entire reason a lightweight system is selected
What changes density within a material
Published density figures are ranges because the material is made, not bought.
In cementitious composites, density falls with entrapped air and rises with compaction. Sprayed and roller compacted material sits at the top of the range; poorly compacted material sits lower and is also weaker and more absorbent, so a low density result on a test coupon is a quality signal rather than a benefit. Mix design matters too: lightweight aggregate, air entrainment and higher polymer content all reduce density.
In polymer laminates, density is set by fibre volume fraction, because glass at around 2,550 kg per cubic metre is considerably denser than cured polyester or vinyl ester resin at around 1,100 to 1,200. A laminate with more glass is denser, stronger and stiffer. Voids reduce density and reduce strength at the same time, so density is used as a rapid quality check on laminate consolidation.
Moisture content affects measured density in cementitious and gypsum materials, which is why test methods specify whether the specimen is oven dry or saturated and why density and water absorption are normally measured on the same coupon.
Using density honestly in a comparison
Material comparisons on density alone are misleading in both directions. A denser material is not worse; ultra high performance concrete is denser than ordinary concrete and produces lighter elements because it can be made thinner. A less dense material is not automatically lighter in service; a thick FRP sandwich panel with a deep core can weigh more per square metre than a thin cementitious skin.
The honest comparison is weight per square metre of the finished panel, at the geometry the project actually requires, including ribs, frame and fixings. That number should come from the manufacturer against the project panel schedule rather than from a material data sheet. It is also the number to use when checking strength to weight ratio and dead load, and the number the structural engineer should be given at the earliest possible stage, because a change to it late in design propagates into the substructure and sometimes into the structure.
Standards and references
- BS EN 1170-6 Test method for glass-fibre reinforced cement, Determination of the absorption of water by immersion and determination of dry density
- ASTM C948 Standard Test Method for Dry and Wet Bulk Density, Water Absorption, and Apparent Porosity of Thin Sections of Glass-Fiber Reinforced Concrete
- ISO 1183 and ASTM D792, density of plastics and composites
- ASTM D2734, void content of reinforced plastics, which is derived from density
- AS/NZS 1170.1 Structural design actions, permanent, imposed and other actions (dead load)
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products
Where this matters on a ShapeShift project
One Sydney Harbour, Barangaroo: A high rise residential tower where panel weight per square metre governs the substructure, the craneage and the load carried down through the building, not the density of the material on its own.
Related terms
Questions specifiers ask
What is the density of GRC?
Typically 1,900 to 2,100 kg per cubic metre for sprayed material at 28 days, only slightly below normal weight concrete. The weight saving in a facade comes from thickness, not from density.
Why is a GRC facade so much lighter than precast if the density is similar?
Because there is no steel in the skin, so no cover is required and the panel can be 10 to 20 mm instead of 100 to 150 mm. ShapeShell-RC is published at 30 to 50 kg per square metre against roughly 360 for a 150 mm precast panel.
Which number should be given to the structural engineer?
Weight per square metre of the finished panel including ribs, frame and fixings, taken from the project panel schedule. Material density on its own is not enough to design a substructure.
Does a lower density mean a better panel?
No. In a cementitious composite, low density usually means poor compaction, which also means lower strength and higher water absorption. Density is used as a quality indicator, not as a performance target.
How does panel weight affect installation?
It sets crane class and lift radius, which sets the maximum panel size, which sets the number of panels and therefore the installation duration. Lighter panels also allow smaller brackets and fewer thermal bridges.
ShapeShell-RC is published at 30 to 50 kg/m², ShapeShell-RT at 5 to 32 kg/m². Compare against your structure before the substructure is designed. Use the facade calculators
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.