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There are other methods of determining this initial firmness. This method, however, has been accepted by the furniture industry. The second physical measurement is the Compression Modulus, sometimes called Sac Factor or Sag Factor. It is an approach to measuring the deeper feeling of firmness. It is the relationship be- tween an ILD value taken at 25% deflection and a second ILD value taken at 65% deflection. Our drawings indicate this relationship. There is a normal value for the 65-25% relationship for each type of foam made. In general, the higher the density of a foam, the higher the Compression Modulus. Higher density foams allow lower 25% ILD values to be used and lower density foams require higher 25% ILD values. This change is due in part to the way the second physical mea- surement, Compression Modulus, contributes to the "Feel Of Com- fort" and varies with the density. For a 1.25 density foam the 65% ILD value will be approximately 1.80 times the 25% ILD. A 3.25 density reinforced foam will have a modulus of 2.30. Here we have two different foams. One has a higher Compression Modulus. Both foams, however, have the same 65% ILD value. The 25% value must be lower for the foam with the higher Compression Modulus. For example, a foam with a 1.80 Compression Modulus has a 65% ILD of 58 pounds. Its 25% ILD is 32 pounds. The heavy density rein- forced foam also has a 65% ILD of 58 pounds. The 25% ILD is 25 pounds and its Compression Modulus is 2.3. The cushion with lower 25% ILD will have the more luxurious "Feel Of Comfort' particularly with todays trend to high crown cushions. Encasing a foam in a softer material such as polyester fiber accom- plishes the same purpose. The 25% ILD is reduced and the foam core contributes the load carrying to give the "Feel Of Comfort." This leads us to the third factor of the term "Feel Of Comfort'. This is hysteresis, or the rubbery push-back feeling of firmness. Hysteresis is the relationship of the initial 25% ILD value measured on the downward cycle to the 25% ILD value measured on the return or upward cycle. This value is measured after the 65% ILD measure- ment. The returning 25% value is always less than the initial 25% ILD. It is expressed as a percent loss. The measurement of this loss is important not only as a measurement of comfort; the value obtained can also indicate the degree of softening, and cushion distortion that can be expected in use. 8