Hi Kbxy88,
Dreamfoam is correct that the durability/quality of polyfoam is best expressed by the density of the foam (mass per unit volume), and not the ILD / IFD (plushness). Density and ILD/IFD are not necessarily related in polyfoam.
As a consumer, all the information you need to know is in this article. While the specs that affect the quality and durability of the layers and components are important to know, I would consider ILD/IFD information to be a legitimate part of what many manufacturers consider to be “proprietary” information and it can add to the confusion for most consumers anyway. I would also keep in mind that ILD is only one of several variables or “specs” that will determine how soft or firm an individual layer or a mattress “as a whole” will feel to different people (see post #4 here). Many mattress manufacturers also are aware that people attempt to copy their designs with DIY componentry, so disclosing ILD/IFD is something they choose not to do, as eventually your own personal testing will tell you more about the appropriateness of any product for your needs than ILD specs.
Phoenix