CMP seat base size?

[Grant Bowker]

I have noticed that some vendors describe their foam's firmness in terms of what weight applied to a 50 sq.in. area is required to achieve 25% compression of a 4" sample rather than soft/firm. The loads stated vary from 15 up to 90 pounds (maybe a wider range?. Since this is a static load and bumps make a dynamic load (perhaps 2-3G???) I was thinking a seat base should be at least mainly the firmest foam I could find. Did any of the people with experience of foam use foam number rated in the way I described and if so, what was the Indentation Load Deflection, or ILD number? I prefer a numeric system over "soft" or "firm" as the words can mean different things to different people but a properly defined numeric system should mean the same thing in every case.