Mineral wool is an insulation material made from thin fibres of molten rock (rock wool) or glass (glass wool). The fibres form an open structure that traps air, and still air is an excellent insulator. Mineral wool is the most widely used insulation material in construction.
Rock wool vs. glass wool
| Property | Rock wool | Glass wool |
|---|---|---|
| Raw material | Basalt (volcanic rock) | Recycled glass + sand |
| Fire resistance | Very good (melting point >1000°C) | Good (melting point ~700°C) |
| Sound insulation | Better (higher density) | Good |
| Weight | Heavier | Lighter |
| Price | Slightly higher | Slightly lower |
| Lambda (λ) | 0.034-0.040 | 0.032-0.040 |
Both are excellent insulation materials. Rock wool is slightly better for sound and fire, glass wool is lighter and cheaper.
Where is mineral wool used?
| Application | Type | Thickness (indicative) |
|---|---|---|
| Timber frame (between studs) | Glass wool or rock wool | 90-140 mm |
| Roof (between rafters) | Glass wool | 120-200 mm |
| Knee wall | Rock wool or glass wool | 100-120 mm |
| Cavity wall | Rock wool (injection) | 50-100 mm |
| Interior wall (sound) | Rock wool | 50-70 mm |
| Floor (between joists) | Glass wool | 100-150 mm |
Mineral wool for DIY projects
Mineral wool is the easiest insulation material to install yourse
lf:
1. Cut to size — With a long knife or insulation knife. Cut 1-2 cm wider than the space between the battens, so it fits snugly.
2. Friction fit — The batt fits snugly between the studs/battens thanks to the slightly oversized cut. No glue or fasteners needed.
3. Vapour barrier — Vapour-tight membrane on the warm side, vapour-open membrane on the cold side.
Safety
- Wear gloves — The fibres prick the skin
- Dust mask — Do not inhale the fibres (P2 mask)
- Long sleeves — Avoid skin contact
- Shake out clothing — After work, remove fibres from clothing
Mineral wool vs. PIR
| Mineral wool | PIR | |
|---|---|---|
| Lambda (λ) | 0.035 | 0.023 |
| R-value at 100 mm | 2.86 | 4.35 |
| Fire resistance | Excellent | Moderate |
| Sound insulation | Good | Moderate |
| Price per m² | Lower | Higher |
| Installation | Friction fit | Glue/screw |
| Moisture sensitive | Yes (loses effectiveness) | No |
Mineral wool is cheaper but you need more thickness for the same R-value. PIR is thinner but more expensive.
Related terms
- PIR insulation
- R-value
- Vapour-open membrane
- Vapour barrier
- Battens