Thermal Conductivity
The thermal conductivity λ (lambda) is a material property. It indicates the heat flow that passes through a 1 m² large and 1 m thick layer of material at a temperature difference of 1 Kelvin (K). The unit is W/(mK). The lower the thermal conductivity, the better the insulating capacity.
As a laboratory value, the lambda value refers to dry components. Since water is a good conductor of heat, the thermal conductivity of insulating materials depends on the moisture content.
The following test standards are the used to determine the thermal conductivity of insulation materials.
ISO 8301:1991 "Thermal insulation -- Determination of steady-state thermal resistance and related properties -- Heat flow meter apparatus"
This standard outlines the procedure for determining the steady-state thermal resistance (R-value) and related properties of insulation materials using a heat flow meter apparatus. It provides guidelines for measuring the thermal conductivity (k-value) and thermal resistance of materials under steady-state conditions. The focus is on assessing the ability of insulation materials to resist heat transfer over time. This standard is particularly relevant for materials like building insulation, where the goal is to evaluate how effectively the material reduces heat flow.
ISO 8990:1994 "Thermal insulation -- Determination of steady-state thermal transmission properties -- Calibrated and guarded hot box"
ISO 8990 also deals with the determination of thermal properties of insulation materials, but it uses a different testing apparatus called the calibrated and guarded hot box. This standard provides guidelines for measuring thermal transmission properties, including thermal conductivity and thermal resistance. The guarded hot box method is commonly used for larger-scale assemblies like building components (such as walls, roofs, and floors) rather than small-scale insulation samples. This method takes into account the effects of thermal bridges and other complexities associated with real-world construction.
ASTM C518 - Standard Test Method for Steady-State Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus
This ASTM standard is similar to ISO 8301 and outlines the procedure for measuring the steady-state thermal transmission properties of insulation materials using a heat flow meter apparatus.
ASTM C1363 - Standard Test Method for Thermal Performance of Building Materials and Envelope Assemblies by Means of a Hot Box Apparatus
This ASTM standard is similar to ISO 8990 and describes the hot box method for determining the thermal performance of building materials and envelope assemblies under steady-state conditions.
ASTM C177 - Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus
This ASTM standard is related to the measurement of thermal transmission properties using the guarded-hot-plate apparatus, which is similar to the method described in ISO 8302.
