Hi fdb,
The ILD of latex is measured on the original core and then any layers that are cut from the core would have the same ILD rating regardless of how thick they are. The ILD isn’t retested for individual layers once the original core is tested.
In the case of Dunlop … the top can be firmer than the bottom of the core so a 3" layer that comes from the top half of a core can be softer than a 3" layer cut from the same core that comes from the bottom half even though they would both have the ILD rating of the original core.
ILD is also also only one of the specs that creates the sensation of the softness or firmness of a layer (see post #4 here).
I would also be aware that ILD can be tested in different ways (most commonly at 25% compression but in some cases at 40% compression) and that the thickness of the original core that is tested will also have a significant effect on the ILD rating and ILD may not always be comparable between different materials or different types of latex (see post #6 here)
Phoenix