The higher the sag factor, the better the foam. The sag factor on most foams around today range from a low of 2.0 to a high of 3.0. Any foam having a sag factor less than 2.0 is usually a poor quality foam which would most likely indicate that it was poorly formulated. Fatigue loss is a means of determining what will happen to a cushion in service. Basically It enables one to determine what the height loss and compression loss would be after it has been in service for some time.
Hysteresis loss is relative to compression readings.
If it does, generally there is something else wrong as well. Tensile, Elongation, Tear are three tests of foam quality. They are a simple way to determine the mechanical strength of a piece of foam. Tensile strength is the force required to pull apart a piece of foam and is expressed in pounds per square inch. Elongation is the amount the same piece of foam will stretch before it does pull apart.