Sandwich Panel U-Value Calculator
This U-value calculator estimates the thermal transmittance of any Real Panel core and thickness in seconds — then get the declared figure for your project from our technical desk.
PIR core · λ = 0.022 W/m·K · surface Rsi+Rse = 0.17 m²K/W
How this U-value calculator works
A sandwich panel's thermal performance comes almost entirely from its insulating core. The thin steel facings add no meaningful resistance, so the calculation reduces to the core, its thickness and the standard surface resistances.
The terms
U — thermal transmittance, in W/m²K (lower is better).
d — core thickness, in metres (e.g. 100 mm = 0.10 m).
λ — thermal conductivity of the core, in W/m·K.
Rsi, Rse — internal and external surface resistances, set by the application per EN ISO 6946.
Core conductivity (λD)
| Core material | Typical λD (W/m·K) |
|---|---|
| PIR | 0.022 |
| PUR | 0.023 |
| EPS | 0.038 |
| Rockwool | 0.041 |
Surface resistances
| Application | Rsi | Rse | Total |
|---|---|---|---|
| Wall (horizontal) | 0.13 | 0.04 | 0.17 |
| Roof (upward) | 0.10 | 0.04 | 0.14 |
Good to know
Values follow EN ISO 6946; declared core λD values follow EN 14509, the European standard for sandwich panels. Results here are indicative for the clear panel area — real assemblies also include small thermal bridges at fixings and joints. For specifications, always use the product datasheet.
These λ values are typical reference figures. Confirm against the declared values on each Real Panel product datasheet — see Performance Data or Product Catalogs.
Need declared values for your project?
Send us the panel type, thickness and application — our technical desk returns the declared U-value, the datasheet and the relevant test references.