4.1 The thermal resistance, R, of an insulation is used to describe its thermal performance.

4.2 The thermal resistance of an insulation is related to the density and thickness of the insulation. It is desirable to obtain test data on thermal resistances at thicknesses and densities related to the end uses of the product.

4.3 In normal use, the thickness of these products range from less than 100 mm (4 in.) to greater than 150 mm (6 in.). Installed densities depend upon the product type, the installed thickness, the installation equipment used, the installation techniques, and the geometry of the insulated space.

4.4 Loose-fill insulations provide coverage information using densities selected by manufacturers to represent the product installed densities. Generally, it is necessary to know the product thermal performance at a representative density.

4.5 When applicable specifications or codes do not specify the nominal thermal resistance level to be used for comparison purposes, a recommended practice is to use the Rsi (metric) = 2.65 m F/Btu]) label density and thickness for that measurement.

4.6 If the density for test purposes is not available from the coverage chart, a test density shall be established by use of applicable specifications and codes or, if none apply, agreement between the requesting body and the testing organization.

4.7 Generally, thin sections of these materials are not uniform. Thus, the test thickness must be greater than or equal to the product's representative thickness if the results are to be consistent and typical of use.

Note 1: The representative thickness is specific for each product and is determined by running a series of tests in which the density is held constant but the thickness is increased. The representative thickness is defined here as that thickness above which there is no more than a 2 % change in the resistivity of the product. The representative thickness is a function of product blown density. In general, as the density decreases, the representative thickness increases. Fortunately, most products are designed to be blown over a small range of densities. This limited range yields a range of representative thicknesses between 75 to 150 mm (3 to 6 in.) for most products. To simplify the process for this practice, the representative thickness for the C1859 tests is considered 87.5 mm (3 ¹/₂ in). All thermal testing on this product is conducted at a thickness that is greater or equal to the representative thickness.

4.7.1 For this practice, the minimum test thickness shall be 87.5 mm (3 ¹/₂ in.). If the test is to represent an installation at a lesser thickness, the installed thickness shall be used.

4.8 For purposes of this practice, it is acceptable to estimate the thermal resistance at any thickness from the thermal resistivity obtained from tests on the product at the minimum test thickness (see 4.7.1) and at the density expected for the proposed thickness.

4.9 In principle, any of the standard methods for the determination of thermal resistance are suitable for loose-fill products. These include Test Methods C177, C518, C1114, and C1363. Of these test methods, the heat flow meter apparatus, Test Method C518, is preferred because of its lower cost and shorter testing time.

4.10 The thermal resistance of low-density insulations depend upon the direction of heat flow. Unless otherwise specified, tests shall be performed for the maximum heat flow condition, that is, a horizontal specimen with heat flow-up.

4.11 Specimens shall be prepared in a manner consistent with the intended installation procedure. Products for pneumatic installation behind netting shall be pneumatically applied (blown) using the manufacturer's installation instructions and netting specified.