Key Takeaways
- Conductivity rises with temperature, so the mean temperature is the required input. Using the ambient value in a high-temperature design undersizes the insulation by up to 40%. This calculator applies λ = 0.056 + 0.00011t for the standard grade unless you select another.
Frequently Asked Questions
What inputs do I need for the conductivity calculation?
Three: the hot-face temperature, the expected cold-face temperature (or the target heat-loss rate), and the density grade. The mean temperature is the average of hot and cold face — that value drives the conductivity, which is why the calculation iterates: assuming a cold face changes the mean, which changes conductivity, which changes the resulting cold face. Two iterations converge in practice.
Why does the calculator ask for mean temperature rather than operating temperature?
Because thermal conductivity is a function of the mean temperature across the insulation layer, not the process temperature. A pipe carrying 400°C fluid with 75mm of insulation has a mean around 230°C across the layer — and the conductivity at 230°C mean is what determines the heat loss. Quoting conductivity at the process temperature overstates it; quoting at ambient understates it.
Which grade should I select in the calculator?
Use LG-Standard (170-250 kg/m³, coefficient 0.00011) for general industrial insulation, kiln backing, and vessel duty. Use LG-High Temp (250-270 kg/m³, coefficient 0.00012) for 1100°C service. For load-bearing zones requiring high density (800-900 kg/m³), conductivity runs higher and follows approximately λ = 0.095 + 0.00018t — the calculator provides the grade option where applicable.
How accurate is the calculator compared with a batch certificate?
The calculator uses production-average coefficients and gives a design-stage estimate suitable for specification and sizing. Batch certificates carry the measured conductivity for the specific delivered batch per ASTM C518 at stated mean temperatures — those are the compliance figures for your project quality file. Where the design mean exceeds 800°C, request the measured conductivity curve, because the linear model flattens above that range.
How Thermal Conductivity Is Calculated
Verified Manufacturing Data: Mingfa Insulation — established 1991, joint venture with China Building Materials Academy. 108,000 m² facility, ~20 national patents, ISO 9001:2015 certified. Annual capacity: 50,000+ tonnes. Full company profile
For Mingfa LG-Standard (HCS-23) and LG-High Temp calcium silicate insulation boards, thermal conductivity increases linearly with temperature. The relationship follows this formula, established through decades of laboratory testing using the guarded hot plate method (ASTM C518 / GB/T 10294):
Standards: [1] ASTM C533-17(2023); [2] EN 14306:2015+A1:2018; [3] GB/T 10699. Certifications
This formula applies to Mingfa's standard density grade (approx. 230 kg/m³). Different density grades (170-900 kg/m³) have slightly different conductivity curves. For project-specific thermal calculations involving other densities, contact our technical team.
Thermal Conductivity Calculator
Need R-value instead? See our calcium silicate R-value guide for imperial unit conversions.
Reference Values at Common Temperatures
The table below shows pre-calculated thermal conductivity values using the standard formula. These are laboratory-verified reference points for quick lookup.
| Mean Temperature (°C) | Thermal Conductivity lambda (W/m·K) | Notes |
|---|---|---|
| 100 | 0.0670 | Low-temperature industrial pipe insulation range |
| 200 | 0.0780 | Medium-temperature equipment insulation |
| 300 | 0.0890 | Typical for steam piping and process vessels |
| 400 | 0.1000 | Cement kiln preheater tower backup insulation |
| 500 | 0.1110 | Aluminum reduction cell thermal barrier |
| 600 | 0.1220 | High-temperature furnace backup lining |
Understanding the Formula
The linear conductivity model (lambda = 0.056 + 0.00011t) is the standard reference curve for Mingfa calcium silicate products with density around 230 kg/m³. Key points to understand:
- Intercept value (0.056): This is the extrapolated thermal conductivity at 0°C. In practice, measurement at very low temperatures introduces higher uncertainty; the formula is most reliable between 100°C and 650°C.
- Slope (0.00011): The rate at which conductivity increases with temperature. This is a material property of the xonotlite crystal phase.
- Higher-density grades (such as MF-HD at 800-850 kg/m³) have somewhat higher conductivity values because denser materials conduct more heat. Contact our technical team for grade-specific conductivity curves.
- Lower-density grades (such as HCS-17 at 170 kg/m³) have slightly lower conductivity but reduced compressive strength, trading off thermal performance against mechanical loading capacity.
Engineering Note
For thermal calculations, always use the mean temperature of the insulation layer, defined as (T_hot_face + T_cold_face) ÷ 2. This is not the same as the hot face temperature. For example, if the hot face is at 400°C and the cold face is at 60°C, the mean temperature is 230°C, giving lambda = 0.0813 W/m·K.