Hi looking4mattress,
I am not quite understanding your question.
When the ILD is measured for a foam, the general method is to measure the force it takes to compress the block of foam, depressing the 4" block 25% of its thickness or 1".
“ILD, or Impression Load Deflection, is a measure of the softness or firmness of a foam mattress. ILD is measured by pressing a 12-inch round disk into a 4-inch piece of foam until it presses 25% or one inch into the mattress surface. The amount of weight or pressure required to compress the mattress to that extent is the ILD.”
ILD is measured by taking a 15 inch by 15 inch by 4 inch section of foam and measuring the force in pounds that it takes a 50 square inch circular plate to compress the material 25 percent of its thickness. If a foam section requires 36 pounds of pressure to reach 25 percent compression, it has an ILD value of 36
There is also a secondary measurement which is not often talked about which is the amount of force needed to compress the foam at 65% of its thickness. This leads to yet another measurement called the support factor.
Support Factor also known as Compression Modulus. Typically, the more difference between the 25 percent ILD and the 65 percent ILD, the more ability the foam has to support weight. The ratio of the 65 percent ILD divided by the 25 percent ILD is called the foam’s support factor. Support factors for foam range from about 1.5 to 2.6.
Talalay processed latex results in a more uniform distribution of the density of the foam whereas Dunlop processed latex results in a block of foam where the density at the bottom of the block is higher (as the particles/sediment sink to the bottom in the process) than the density at the top of the block. This is why Dunlop is said to be “bottom heavy” and it support factor will be higher than Talalay .
The difference between Talalay and Dunlop is often described as sponge cake vs pound cake. Talalay is also described as being bouncier.
You will get some purists that will insist you have to measure the force in newtons, blah blah blah, and that is technically true, but we are trying to keep it simple and understandable.
Hope this clears things up.
Maverick