A material property is a measurable, numerical characteristic of a building material: density, compressive strength, thermal conductivity, vapour resistance and so on. These figures decide what a material is fit for, and they are published in the declaration of performance and the manufacturer’s technical data sheet.
The properties that matter on site
Mechanical
- Compressive strength (N/mm²) — how much pressure the material can carry. Decisive for concrete, masonry units and load-bearing insulation
- Tensile and flexural strength (N/mm²) — concrete is strong in compression but weak in tension, which is why it is reinforced
- Modulus of elasticity (N/mm²) — how stiff the material is, that is how far it deflects under load
- Density (kg/m³) — governs self weight and, indirectly, the sound insulation of a wall
Building physics
- Thermal conductivity λ (W/m·K) — how readily heat passes through. Mineral wool and PIR are low, metals extremely high
- Vapour resistance factor µ (dimensionless) — how much harder water vapour passes through the material than through air. Critical for vapour control layers and insulation build-ups
- Specific heat capacity (J/kg·K) — how much heat the material stores; important for controlling summer overheating
- Coefficient of thermal expansion — how much the material grows as it warms. Ignore it and the work cracks or binds
Other
- Reaction to fire — European classes A1 to F under EN 13501-1
- Water absorption and frost resistance — decisive for external masonry and facing brick
- Durability class of timber — natural resistance to decay, from class 1 (very durable) to 5
Why they have to be read together
Materials are rarely chosen on one property alone. An insulation board with an excellent lambda but too little compressive strength is unsuitable under a screed. A vapour-tight board on the cold side of a build-up causes interstitial condensation however well it insulates. Always look at the combination of properties the application demands — and use the declared design value, not the most flattering laboratory figure.
Related terms
- Building materials
- Density
- Compressive strength
- Modulus of elasticity
- Fire classification
- Durability class
- Insulation
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