How to choose thermal insulation: lambda values and thickness calculation guide

Thermal insulation performance is governed by precise physics rather than brand prestige. When evaluating building envelope designs or EKR energy efficiency renovation grants, the thermal conductivity coefficient (lambda, λ) and installed thickness determine whether the building meets regulatory U-value thresholds.

Core thermal metrics explained

• Thermal conductivity (λ, W/mK): Material-specific ability to conduct heat. A lower value indicates better insulation per millimeter of thickness.
• Thermal resistance (R = d / λ, m²K/W): Insulation capability of a specific layer thickness (d in meters). Higher R means greater insulation.
• Overall heat transfer coefficient (U = 1 / R_total, W/m²K): Rate of heat transfer through a complete structural assembly. Lower U indicates less heat loss.

Practical calculation: 25 cm ODE Starflex glasswool

For attic floor insulation under Hungarian energy guidelines:

• ODE Starflex glasswool thermal conductivity: λ = 0.039 W/mK
• Installed thickness: 25 cm (0.25 m), typically laid as 2 × 12.5 cm staggered layers
• Thermal resistance of insulation layer: R = 0.25 / 0.039 = 6.41 m²K/W
• Resulting thermal transmittance through insulation: U ≈ 0.156 W/m²K

Adding the interior and exterior surface thermal resistances (Rsi + Rse) and ceiling structure brings the total assembly well within modern near-zero energy building requirements.

EuConX Iso Kft. provides factory-direct ODE Starflex glasswool complete with CE marking, EUCEB fiber safety certification, and EPD environmental declarations.

For thickness calculations and direct truckload supply, contact info@euconx.com or call +36 30 968 6527.