FAQs About Common K Value (Thermal Conductivity) Applications

Engineers and purchasing professionals often need reliable thermal conductivity (K value) data for correct material selection, long-term performance, and cost efficiency. Below are answers to some of the most common questions we receive about Alkegen (formerly Unifrax) products.

Q: K values on the Alkegen Heat Flow Program are listed only to 1600°F. How do I use this information if my application is above 1600°F?

A: K values in the Heat Flow Program are based on mean temperature, not hot face temperature. Temperature drop across a furnace lining is not uniform, and K values vary with temperature.

To calculate mean temperature:

Example:

• Hot Face = 2000°F
• Ambient = 100°F
• Mean = (2000 + 100)/2 = 1050°F

Because a mean temperature above 1600°F would require hot face conditions beyond 3000°F, K values above 1600°F are not applicable for ceramic fiber insulation.

Q: What is the R Value of Durablanket?

A: R Value is most often used in commercial/low-temperature insulation:

• At <500°F: Conduction dominates heat transfer. Lower-density products yield better R values.
• At >1000°F: Radiation dominates. Higher-density products block radiant heat more effectively.

Formula:

Note: Always use the K value corresponding to the mean temperature of your application. While R value can be calculated, it is not a reliable performance measure above 1000°F.

Q: Is there an equation to calculate K values at specific temperatures?

A: Yes. The quadratic curve-fit equation allows you to calculate K at a desired mean temperature (T):

Where A, B, and C are constants (specific to each material) available in the Alkegen Heat Flow Program. These values are derived from regression analysis of multiple data sets.

Example with Durablanket S, 8 pcf at 1000°F mean temp:

• A = 0.361178571429
• B = 0.000069107143
• C = 0.000000684821

K = 0.361178571429 + (0.000069107143 × 1000) + (0.000000684821 × 1000²)

K = 0.9770K = 0.9770K=0.9770

Accurate K values are critical for selecting the right insulation and avoiding costly system inefficiencies.