4.1 The various methods for measuring and calculating thermal properties provide data and information for manufacturer's published information, for comparison of related products, and for designers and users to evaluate insulation products for particular applications. For these purposes it is advisable to provide basic data and information produced under standard temperature conditions.

4.2 It is possible that thermal properties of a specimen will change with mean temperature, with temperature difference across the specimens, and with high temperature exposure. Data and information at standard temperatures are necessary for valid comparison of thermal properties.

4.3 The mean test temperatures to measure thermal properties shall be selected from those listed in Table 1. It is recommended that thermal properties of insulation materials be evaluated over a mean temperature range that represents the intended end use. For this situation, the lowest and greatest mean temperatures need to be within 10°C of the maximum and minimum mean temperature of interest. The temperature differences for any chosen mean temperature will depend upon both the thermal insulation application (see appropriate materials specification), the method of evaluation, and the limitations of the apparatus. Temperature differences or relevant temperature conditions required by ASTM material specifications shall take precedence over those recommended in this practice.

4.3.1 Standard conditions are presented where both surfaces are exposed to fixed ambient temperatures that are typical for testing building constructions, both insulated and uninsulated (Table 2).

4.3.2 Standard conditions are presented where the temperatures of the two surfaces are fixed and surface coefficients are not considered (Table 3).

4.3.3 For conditions where the temperature of only one surface is fixed with the other exposed to fixed ambient temperature, use the mean temperatures of Table 1.

4.4 These conditions must be stated to describe accurately thermal properties such as thermal conductivity versus mean temperature for thermal insulating materials. Thermal insulations exhibiting inflection points due to the change of state of insulating gases (see Note 2), must be tested at sufficiently small temperature differences between (1) the hot and cold sides and (2) between mean temperatures. The test temperature differences used depend on the vapor pressure versus temperature relationship of the gases involved and the ability of the test apparatus to provide accurate measurements of low temperature differences.

Note 2: Certain closed-cell cellular plastic insulations are of this type.

1.1 This practice covers standard mean temperatures for reporting thermal properties of thermal insulations, products, and materials, and of related systems and components, both insulated and uninsulated.

1.2 Thermal properties shall be determined as a function of temperature by standard test methods. (Test Methods C177, C201, C335/C335M, C518, C745, C1114, C1363, Guide C653, and Practice C687, all in combination with Practice C1045.)

Note 1: Standard referenced materials are needed to span the temperature range of the tests.

1.3 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.

1.4 This practice recommends standard conditions for use in testing and evaluating thermal properties as a function of temperature by standard test methods.

1.5 General applications of thermal insulations include:

1.5.1 Building envelopes,

1.5.2 Mechanical systems or processes, and

1.5.3 Building and industrial insulations.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.