4.1 The 25-mm [1-in.] deflection IFD method is recommended for production screening and quality control on full size cushions only.

4.2 Applicable cushion thicknesses to be tested by this test method are only those listed in this test method. Further research and development are required before this test method is applicable to other cushion thicknesses.

4.3 This test method is designed to give a value approximating the 25 % IFD on a 100-mm [4-in.] thick piece of foam when the actual specimen thickness tested is within the ranges listed in the test method. In case of disagreement, the referee method is the IFD procedure in Test Methods D3574, Test B₁. The user of this test method shall establish the correlation between this test method and the referee method.

1.1 This test method covers a screening type quality control test used to determine if flexible polyurethane foam cushions are within the specified grade range for firmness.

1.2 This test method is limited to foams with thicknesses that are 75 mm [3 in.] or greater.

1.3 This test method is based on the fact that the traditional industry standard thickness for Indentation Force Deflection (IFD) is 100 mm [4 in.], and the traditional percent deflection for IFD acceptance and product planning is 25 %. With respect, then, to these traditional industry conventions, a 25 % deflection on a 100-mm [4-in.] cushion would be 25 mm [1 in.]. Thus, deflecting standard cushions (of proper 100 mm thickness) 25 mm [1 in.] provides a quick way to determine if the flexible polyurethane foam is within the specified grade range for 25 % IFD.

1.4 Cushion thicknesses less than 75 mm [3 in.] shall not be tested for IFD using this test method.

1.5 This test method is intended to provide a quick and simple method to screen flexible polyurethane foams for determination of its firmness grade.

1.6 Units—The values stated in U.S. Customary or SI 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.

1.7 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.

Note 1: This test method and ISO 2439 address the same subject matter, but differ in technical content.