What is the density of unidirectional carbon fibre composite?

1,600 kg/m³ (1,550–1,650), or 1.60 g/cm³.

Does unidirectional carbon fibre composite float?

No. At 1,600 kg/m³ it is denser than water.

Unidirectional carbon fibre composite

Density of unidirectional carbon fibre composite

1,600 kg/m³ (1,550–1,650)

1.60 g/cm³ · 99.9 lb/ft³

All the fibres run one way, and so does all the strength: along the fibre it beats every steel per kilogram, across it the strength is that of the epoxy alone, roughly 50 MPa. Real structures are laminated from plies at different angles to get around this, and the lay-up is as much of the design as the shape. It has no melting point — the epoxy matrix softens above its glass transition, typically 120-180 °C, and then decomposes, which is why a carbon frame must never be repaired with heat and why fire is the failure mode aerospace worries about.

Properties

Density: 1,600 kg/m³ (1,550–1,650) — 1.60 g/cm³
Tensile strength: 1500–2500 MPa
Young's modulus: 135 GPa
Floats in water: No
Magnetic: No

What it is used for

Aircraft wing spars and fuselage skins
Bicycle frame tubes and forks
Wind turbine blade spar caps
Prosthetic running blades

How it compares

Water is 1,000 kg/m³. Anything with a shorter bar than water floats in it.

air 1.2 kg/m³

expanded polystyrene foam 20 kg/m³

rigid polyurethane foam 40 kg/m³

Water — the float line 1,000 kg/m³

unidirectional carbon fibre composite 1,600 kg/m³

tungsten 19,250 kg/m³

gold 19,300 kg/m³

platinum 21,450 kg/m³

Water is 1,000 kg/m³. Anything below that floats.
Material	Density	Relative to water
rigid polyurethane foam	40 kg/m³	0.04×
expanded polystyrene foam	20 kg/m³	0.02×
air	1.2 kg/m³	0.00×
unidirectional carbon fibre composite ←	1,600 kg/m³	1.60×
platinum	21,450 kg/m³	21.45×
gold	19,300 kg/m³	19.30×
tungsten	19,250 kg/m³	19.25×

Does it rust?

Unidirectional carbon fibre composite contains no iron, so it cannot rust. Whether it degrades depends on the material, not on oxidation.

Is it magnetic?

Unidirectional carbon fibre composite is not a metal and has no ferromagnetic response.

Common questions

What is the density of unidirectional carbon fibre composite?: 1,600 kg/m³ (1,550–1,650), or 1.60 g/cm³.
Does unidirectional carbon fibre composite float?: No. At 1,600 kg/m³ it is denser than water.
Is unidirectional carbon fibre composite magnetic?: Unidirectional carbon fibre composite is not a metal and has no ferromagnetic response.

Does unidirectional carbon fibre composite float? No
Fibreglass (GRP) 1,900 kg/m³
Woven carbon fibre composite 1,550 kg/m³
Asphalt (hot-mix) 2,350 kg/m³

Sources

Typical range compiled from manufacturer specifications — At One Place

How these figures are compiled and checked