Rogers Corp., Rogers, Conn., reports the hardness characteristics of its Poron family of urethane foams using ASTM D3574. This standard describes procedures for evaluating "Flexible Cellular Materials — Slab, Bonded, and Molded Urethane Foams." In this test method hardness is determined by Compression Force Deflection (CFD), Test C.

CFD is an engineering measurement expressed in pounds-force-per-square inch (psi). It is merely the force required to compress a material a fixed percentage. Rogers Corp.'s High Performance Foams Div. has chosen 25% compression to characterize various grades of Poron microcellular urethanes.

CFD measurements are a useful tool for making

material selections and are also available in compression values other than 25%. The conventional Shore hardness measurements provide only relative information. For example, a material with a Shore "A" 5 rating is softer than one with Shore "A" 10 but says nothing about how much compression force is needed to fill a gap or make a tight seal.