Aluminium Guide · Lesson 08

Aluminium vs steel, PVC and timber

Every material has its place. When aluminium is the right choice, when it is not, and what to bear in mind if you are replacing a part made of another material.

5 minutes’ read

In short

Aluminium weighs a third as much as steel (2.7 vs 7.85 g/cm³) and needs no paint to protect it from corrosion.
It is about a third as stiff as steel (69 vs 205 GPa): to replace steel, the section has to be made larger, and even then it ends up lighter.
Compared with PVC and timber, aluminium is much stiffer and more stable, does not warp in the heat and lasts for decades outdoors.

The comparison in numbers

	Aluminium	Steel	Rigid PVC
Density (g/cm³)	2.7	7.85	1.4
Stiffness, elastic modulus (GPa)	69	205	3
Thermal expansion (µm per metre per °C)	23.4	11.7	70
Thermal conductivity (W/m·K)	200	52	0.16
Critical temperature	Melts at 615–655 °C	Melts at ≈ 1,500 °C	Softens at ≈ 80 °C

Aluminium 6063-T6, SAE 1020 carbon steel and rigid PVC. Reference values; they vary with the alloy and the manufacturer.

Aluminium vs steel

In favour of aluminium: it weighs a third as much, does not rust or need paint, can be extruded into complex shapes in a single step (channels, interlocks, fins) and can be recycled without losing quality.
In favour of steel: it is stiffer and stronger for the same section, and it withstands fire and high temperatures better.
When replacing a part: so that it does not deflect more, the aluminium profile needs more depth or more material than the steel one. With a well-designed section, it is still usually 40 to 50% lighter.

Aluminium vs PVC and timber

Stiffness: aluminium is about 20 times stiffer than PVC. That is why aluminium windows and doors have slimmer profiles and can take larger glazed panels; PVC needs steel reinforcement inside.
Heat and sun: PVC expands about three times as much as aluminium and softens at around 80 °C. Timber swells with moisture and needs regular varnishing. Aluminium is stable.
Insulation: here PVC and timber win, because aluminium conducts heat very well. The solution is windows and doors with a thermal break (known in Argentina as RPT): two aluminium profiles joined by an insulating element that blocks the flow of heat.
Durability: aluminium lasts for decades outdoors with nothing more than cleaning, and at the end of its life it is fully recycled.

Frequently asked questions

Which is better for windows, aluminium or PVC?

Aluminium is stiffer, allows slimmer profiles and larger glazed panels, and does not warp in the sun. PVC insulates better on its own; with a thermal break (RPT), aluminium insulates much better, although a PVC frame usually still insulates slightly more.

How much lighter is aluminium than steel?

The same part weighs 66% less, because the density of aluminium is 2.70 g/cm³ and that of steel is 7.85 g/cm³. If the section is redesigned for the same stiffness, the saving is usually between 40 and 50%.