📊 Conductivity (λ) and thickness by material
Lower λ = better insulator (thinner for the same performance). Thickness shown to reach a wall U ≈ 0.24 W/m²K:
| Material |
λ (W/mK) |
≈ thickness for U 0.24 |
| PIR / PUR | 0.024 | ~10 cm |
| Glass wool | 0.032 | ~13 cm |
| XPS | 0.033 | ~13 cm |
| Mineral wool / EPS | 0.035 | ~14 cm |
| Wood fibre | 0.040 | ~16 cm |
📐 Formula
R = thickness (m) ÷ λ (W/mK). U = 1 ÷ (Rsi + R + Rse), where Rsi/Rse are the inside/outside surface resistances (wall ≈ 0.13 + 0.04). Lower U = better. Packs = ⌈area × (1 + waste%) ÷ coverage per pack⌉.
🌍 Naming around the world
Insulation = aislación / aislamiento = Dämmung · Mineral wool = lana mineral = Mineralwolle · U-value = valor U = U-Wert · R-value = valor R = R-Wert · Conductivity λ = conductividad = Wärmeleitfähigkeit · Thermal bridge = puente térmico = Wärmebrücke.
❓ Frequently Asked Questions
How many packs of insulation do I need?
Divide the area to insulate (plus waste) by the coverage per pack, and round up. For 15 m² with 5% waste = 15.75 m², and packs of 4.5 m², you need 4 packs.
What is the U-value and what value do I need?
The U-value (W/m²K) is how much heat passes through — lower is better. German GEG new-build targets are about U ≤ 0.24 for walls, ≤ 0.20 for roofs and ≤ 0.30 for floors.
How thick should the insulation be?
It depends on the material: R = thickness ÷ λ. Mineral wool (λ ≈ 0.035) needs ~14 cm for the wall target; PIR (λ ≈ 0.024) needs ~10 cm for the same result.