Insulation Material Comparison
| Material | K-factor | Unit | Thickness (in) | R/in | Total R | Target R | Required in | Difference | Action |
|---|
Formula Used
Imperial K-factor: R-value per inch = 1 ÷ K.
SI conductivity: R-value per inch = 0.144227909 ÷ k in W/(m·K).
Total resistance: Total R = R per inch × effective thickness in inches.
Required thickness: Target R ÷ adjusted R per inch.
Heat transfer: Q = area × temperature difference ÷ effective assembly R.
How to Use This Calculator
- Select the conversion or sizing mode.
- Enter the K-factor, R-value, thickness, and units.
- Add installation adjustments when they apply.
- Complete heat-loss fields for an optional estimate.
- Select Calculate and review every result step.
- Copy, export, or print the finished calculation.
Example Data
| Material example | Imperial K-factor | Approximate R per inch | R at 3.5 inches |
|---|---|---|---|
| Fibreglass batt | 0.27 | 3.704 | 12.963 |
| Mineral wool | 0.25 | 4.000 | 14.000 |
| Expanded polystyrene | 0.24 | 4.167 | 14.583 |
| Polyisocyanurate | 0.16 | 6.250 | 21.875 |
These values are demonstrations only. Temperature, ageing, density, moisture, facing materials, and test methods can change actual thermal performance.
Understanding K-Factor, R-Value, and U-Factor
K-factor measures how easily heat passes through a material. Lower values normally indicate better insulation performance. Always confirm the selected unit before calculating.
R-value measures resistance to heat flow through a layer. Greater thickness generally produces a greater total R-value. Installation quality can reduce expected field performance.
U-factor measures heat transfer through an entire assembly. It is the reciprocal of total assembly resistance. Thermal bridges can raise actual heat transfer significantly.
Frequently Asked Questions
1. What is a thermal-conductivity K-factor?
It describes a material's ability to conduct heat. A lower K-factor generally indicates stronger insulating performance.
2. What does R-value per inch mean?
It is the thermal resistance provided by one inch. Multiply it by installed thickness for total resistance.
3. How is K-factor converted to R-value?
For imperial K-factor units, divide one by K. SI conductivity requires a unit conversion before inversion.
4. Is a lower K-factor better?
Lower K-values mean less heat travels through material. That usually creates a higher R-value per inch.
5. Is a higher R-value better?
Higher R-values resist heat flow more effectively. Assembly design and installation still influence real performance.
6. Why does thickness affect total R-value?
Thermal resistance increases with material thickness. Compressed insulation can lose effective thickness and resistance.
7. Can W/(m·K) convert directly into R-value?
Yes, after accounting for layer thickness and units. The calculator converts SI conductivity into imperial resistance.
8. What is the difference between K-factor and U-factor?
K-factor describes material conductivity. U-factor describes heat transfer through a complete building assembly.
9. Can insulation R-values be added?
Layer R-values can often be added in series. Framing, fasteners, gaps, and bridges require additional analysis.
10. Does temperature affect thermal conductivity?
Many materials change performance with temperature. Use product data matching the expected operating conditions.
11. Why may manufacturer values differ?
Products vary by density, blowing agent, facing, ageing, and testing. Use certified data for final decisions.
Important Limitations
This calculator provides theoretical estimates from entered values. It does not replace laboratory testing or professional building analysis.
Moisture, ageing, temperature, installation gaps, and compression can change performance. Thermal bridges may strongly reduce whole-assembly resistance.
Use verified manufacturer data and applicable building standards. Confirm critical decisions with a qualified professional before construction.