Hi fall0utz,
The density of latex (most often used for Dunlop latex and in Kg/M3) is mentioned quite often on this site, but the relationship between ILD and density in latex is different from that in polyfoam, and as all latex is generally considered to be a high quality and durable material, the ILD tends to be the more important variable to know, along with the type (Dunlop or Talalay) and approximate blend (the percentage of natural rubber and synthetic rubber) of any latex layers.
To further clarify:
In polyfoam, density is mostly independent of the softness or firmness of a foam material (both low and high densities can be made in a full range of firmness and softness levels) although they are very loosely related (in the same “variety” of foam … then much firmer is often a little higher density than much softer but not always). Density though is the single biggest factor in the quality and durability of polyfoam and memory foam. So, density and ILD are separate items that are useful to know about the quality and softness of polyfoam.
With latex, all types of latex are generally considered high quality materials and there is a mostly direct relationship between density and firmness (higher density = higher ILD).
Talalay latex is usually accurately measured, or at least it’s within a fairly narrow range, of the listed ILD. For Talalay, the higher ILD’s use proportionally more latex (are denser), so knowing the ILD will tell you of the softness of the product. Knowing the density isn’t necessary for determining quality/durability like in polyfoam (but it is sometime provided), as we know there is an almost straight-line relationship between ILD and density in Talalay latex. And the latex produced in foam cores is very consistent from top to bottom because of the unique Talalay process.
Contrast this with Dunlop latex, which is more often listed by density (Kg/M3) and “word ratings” rather than ILD. With Dunlop it’s probably more accurate to compare by its density than by its ILD, as there can be variations from the foam slit off the top versus the bottom of a Dunlop core, as there can be particulate settling during the Dunlop formation process. Dunlop densities typically vary between 55 to 95 kg/m³.
Either ILD in Talalay, or ILD (if it’s accurate) or density for Dunlop (see post #2 here as a reference), would probably be the best way to compare relative firmness between different Dunlop layers and sources if they are the same type and blend of latex. If two layers are a different type or blend of latex then ILD ratings may not be comparable between different layers.
In the end, for a piece of latex, the firmness of the mattress is correlated to density - the more material is used, the firmer the mattress is. Hardness is the resistance against exerted pressure. Hardness and density (mass per unit volume) of latex mattresses are related or connected to each other, which is not necessarily the case with polyfoam.
I hope that helps out.
Phoenix