What Is the R-value of Calcium Silicate Insulation?
Calcium Silicate Does Not Have a Single R-value
Calcium silicate insulation does not have a single R-value. Its thermal resistance (R-value) depends on thickness and mean temperature. R-value is the imperial unit equivalent of thermal resistance, commonly used in North America and the UK. It measures how well a material resists heat flow: the higher the R-value, the better the insulation. R-value is calculated as:
R = t / k
Where t is thickness in inches, and k is thermal conductivity in BTU per inch per hour per square foot per degree Fahrenheit (BTU·in/hr·ft²·°F). This is the imperial equivalent of the metric thermal conductivity lambda expressed in W/m·K.
Converting Metric Thermal Conductivity to Imperial
The key conversion factor between metric and imperial thermal conductivity units is:
1 W/m·K = 6.933 BTU·in/hr·ft²·°F
Mingfa's thermal conductivity formula for standard calcium silicate boards (density approximately 230 kg/m³) is:
λ = 0.056 + 0.00011t W/m·K
To convert this to imperial k-value at a given temperature in degrees Fahrenheit, first convert the mean temperature to Celsius, calculate lambda, then multiply by 6.933 to get k in BTU·in/hr·ft²·°F. Divide the thickness in inches by k to obtain the R-value.
R-value Table at Common Temperatures
The table below shows R-values for Mingfa standard calcium silicate boards at common operating temperatures, calculated from the thermal conductivity formula above. Values are provided for 1-inch and 50mm (approximately 1.97 inches) thicknesses, the two most common specifications for international orders.
| Mean Temperature (°F) | Lambda λ (W/m·K) | k (BTU·in/hr·ft²·°F) | R-value at 1 inch | R-value at 50mm |
|---|---|---|---|---|
| 100 | 0.060 | 0.417 | 2.40 | 4.72 |
| 200 | 0.066 | 0.460 | 2.18 | 4.29 |
| 400 | 0.078 | 0.544 | 1.84 | 3.62 |
| 600 | 0.091 | 0.629 | 1.59 | 3.13 |
How to Use These R-values
R-value decreases as temperature rises because calcium silicate thermal conductivity increases with temperature. This is normal behavior for all porous insulation materials. When specifying insulation for a project, use the R-value at your expected mean temperature, not the R-value at room temperature. The mean temperature is the average of the hot face and cold face temperatures of the insulation layer.
For most calcium silicate products on the market, the R-value per inch at moderate temperatures (around 75°F to 200°F) ranges from approximately 0.8 to 1.2. Mingfa products at typical industrial operating temperatures fall within this range, though exact values depend on the specific density grade and operating conditions.
Note that R-value alone does not tell the full story for high-temperature industrial insulation. Calcium silicate boards are chosen for their combination of thermal resistance, compressive strength, dimensional stability, and non-combustibility at temperatures where other insulation materials fail. R-value is one part of the material selection decision, not the only one.
R-value for Different Thicknesses
Because R-value is directly proportional to thickness, you can calculate the R-value for any thickness by multiplying the per-inch R-value by the thickness in inches. For example, a 50mm board (1.97 inches) at 200°F has an R-value of approximately 2.18 x 1.97 = 4.29. For custom thickness calculations or project-specific thermal analysis, use our thermal conductivity calculator to compute lambda at your exact mean temperature, then convert using the formula above.