If I'm looking at foam that has a density of 1.3, and an ILD of 36, and another piece of foam that has a density of 2.8 and an ILD of 36, what exactly is the difference? I know that ILD tells the firmness, but i thought firmness was dependent on the density...? Are these two pieces of foam similar in firmness but one will break down more quickly over time?

Thanks!

(Specifically, trying to figure out eggcrate topper for mattress...The super-soft (1.2, ILD 12) sounds nice, but i'm afraid it's too soft...But the others all have much higher ILD's (though not necessarily higher densities..i.e. 1.3, ILD 36))