Hi TheSleeplessCat,
This is exactly correct. Talalay in the same ILD as Dunlop will be less dense (will weigh less than Dunlop per cubic foot of material) because it has more air in it. This is the basis for the angel food cake vs the pound cake analogy.
Talalay is also more open celled than Dunlop and would be more breathable.
Resilience is a measure of how high a steel ball dropped on a material will bounce expressed as a percentage of it’s original height. It is somewhat opposite to hysteresis which is how much energy it absorbs (called hysteresis). Both Talalay and Dunlop are highly resilient but Talalay has greater resilience (a ball will bounce higher) and springs back more powerfully while Dunlop has less hysteresis (it absorbs less energy overall but it doesn’t decompress as strongly). The biggest difference between them is what is called compression modulus. This is a measure of how quickly a foam gets firmer as it is compressed more. ILD is generally (but not always) a measure of how much weight it takes to compress a foam by 25% of it’s thickness. At compression depths less than this Dunlop will be softer (compress more with the same weight) while at compression depths more than this Dunlop will be firmer (compress less with the same weight). They have a different response curve in other words and since Dunlop gets firmer faster than Talalay … even though the different response curves may cross at the 25% compression level … beyond this Dunlop will not compress as much as Talalay which is why it is generally considered more supportive or “firmer”. Another way to say this is that Dunlop starts off softer and then ends up (at compression levels more than 25%) firmer than Talalay.
This is also part of the reason that Talalay is considered to be more “springy” or “lively” than Dunlop because you will generally sink in deeper which means there is more up and down “movement” or “ride” with Talalay and it springs back more strongly and quickly. This creates a different “feel” between the two materials and is also why Talalay is often considered to be more pressure relieving than Dunlop because it allows for a deeper cradle in the same ILD … while Dunlop is considered to be more supportive because it doesn’t compress as deeply with greater weight … all else (including ILD) being equal of course. Some people will prefer the feel of one over another and because each has different firmness levels available … one is not “necessarily” better than another in either pressure relief or support layers if the right layering or ILD is chosen for each … but you may need to choose a softer ILD with Dunlop than with Talalay to get similar pressure relief in the comfort layers or a firmer Talalay vs Dunlop to get similar levels of support in the support layers. A “one step” difference in ILD which would be about 4 - 5 ILD would be “in the range” for most people where they felt similar.
This video may also be helpful to give you some visual cues about the difference between them.
There is also more about the different types and blends of latex in this article and in post #6 here.
Don’t forget that the layer you are choosing is the comfort layer and that the support layers or “deep support” of both use the same high-density polyfoam. The comfort layers have a primary role of pressure relief and only have a “secondary” support role which is to fill in the gaps in the body profile.
I know it’s difficult to describe what is really a subjective preference but hopefully, this will help you “imagine” how each may feel without having direct comparative experience with both.
Phoenix