This standard specifies the laboratory method for determining the steady-state thermal conductivity of thermal insulation materials using a guarded hot plate apparatus. It is a primary, absolute method that establishes a one-dimensional heat flow across a flat specimen to calculate its intrinsic heat transfer property. The results are fundamental for evaluating and comparing the performance of insulation materials.
Describes the guarded hot plate method for determining the thermal conductivity of insulation materials.
Quick Reference Values
Typical Hot-Face to Cold-Face Temperature Difference20 to 50 °C
Steady State Condition RequirementHeat input variation < 1% over a period
Specimen Flatness RequirementSurfaces shall be flat to within 0.25 mm
Apparatus Metering Area SizeTypically 150x150 mm to 300x300 mm
Recommended Specimen ThicknessNot exceeding one-third of the metering area width
Key Formulas
λ = (q * L) / (A * (t1 - t2)) — Formula for Thermal Conductivity
Practical Notes
This is a precise but time-consuming laboratory test; achieving the required thermal steady-state can take several hours.
The accuracy of the result is highly dependent on minimizing lateral heat loss (the function of the 'guard' heater) and precise measurement of power, thickness, and temperature.
The test is applicable to homogeneous, flat slab materials. Loose-fill or reflective insulations require different test methods.