Calculate insulation resistance from conductivity and thickness. Review U-value, heat loss, and target thickness quickly. Export usable results for engineering checks and retrofit planning.
| Material | Conductivity (W/m·K) | Thickness | Material RSI | Approx. US R |
|---|---|---|---|---|
| Mineral Wool Board | 0.037 | 100 mm | 2.703 | 15.348 |
| Expanded Polystyrene | 0.036 | 75 mm | 2.083 | 11.828 |
| Polyisocyanurate | 0.025 | 50 mm | 2.000 | 11.357 |
| Softwood Panel | 0.120 | 25 mm | 0.208 | 1.182 |
Material RSI = (Thickness in meters × Number of layers) ÷ Adjusted conductivity
Adjusted conductivity = Conductivity × (1 + Correction % ÷ 100)
Total RSI = Material RSI + Internal surface RSI + External surface RSI
U-Value = 1 ÷ Total RSI
Heat Flux = U-Value × Temperature difference
Total Heat Loss = Heat Flux × Area
US R-Value = Total RSI × 5.678263337
Required Thickness = (Target material RSI × Adjusted conductivity) ÷ Layers
Thermal conductivity shows how quickly heat moves through a material. Lower conductivity usually means better insulation. However, conductivity alone does not describe assembly performance, because thickness changes the total resistance strongly.
R-value rises as thickness increases. Two materials with the same conductivity will not deliver the same resistance if their thickness differs. This is why practical envelope design always checks both conductivity and installed depth.
Inside and outside film resistances add small but useful thermal resistance. These values are often included in wall, floor, roof, and facade calculations when engineers estimate full assembly U-values rather than material-only performance.
Installed conditions can change effective performance. Moisture, compression, fasteners, and workmanship may increase heat transfer. A correction factor lets you run conservative checks and compare ideal values with more realistic site conditions.
Total RSI and US R-value represent resistance. Higher values are better for insulation. U-value, heat flux, and total heat loss represent transmission. Lower values are better when you want to reduce heating or cooling demand.
Thermal conductivity measures how easily heat moves through a material. A lower value means the material resists heat flow better, which usually improves insulation performance for the same thickness.
RSI is the metric thermal resistance unit, expressed as m²·K/W. US R-value uses h·ft²·°F/Btu. This calculator shows both and converts between them automatically.
R-value is directly proportional to thickness when conductivity stays constant. Doubling thickness roughly doubles material resistance, which lowers the final U-value and heat flow rate.
Include surface film resistance when you want total assembly resistance instead of material-only resistance. It helps when estimating wall, roof, or floor U-values under standard boundary assumptions.
It adjusts the entered conductivity upward or downward. Use it to model site conditions, moisture effects, compression, or safety allowances during preliminary engineering checks.
Yes. Enter area and temperature difference. The tool calculates heat flux per square meter and total heat loss through the selected surface using the computed U-value.
Enter the target value and select its unit. The calculator estimates the thickness needed for the chosen conductivity and also shows the additional thickness beyond the current input.
It is useful for screening, comparison, and design checks. Final compliance work may require tested product data, framing effects, air gaps, moisture conditions, and project-specific standards.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.