Hi Manimal,
I completely agree that ILD specs can be perplexing and confusing … especially when you are trying to compare different types or blends of latex or different materials or in some cases the same type of material that is made by different manufacturers (see post #6 here). The ILD of a material (including latex) is never exact and is also only one of the factors that can affect the softness or firmness of a mattress or an individual layer (see post #4 here). In some cases a manufacturer may list approximate ILD information that covers a range that would apply to different materials because they know that smaller differences in ILD (less than about 4 ILD or so) aren’t something that most people would be able to tell the difference anyway. Unless you have a great deal of experience with testing or sleeping on different combinations of materials you may not have the personal reference points to “translate” ILD information into something meaningful that will tell you how certain combinations of materials will actually feel to you and focusing on ILD alone can often be more misleading than helpful.
Phoenix