I read somewhere (I don’t recall exact where, but on a manufacturer website), that an ILD rating of the same number for talalay and dunlop latex actually are of different firmnesses. Specifically, talalay with the same ILD as dunlop latex is softer. Is that true? I am trying to decide what firmness will work best for me, and whether I should go with dunlop latex or a top layer with talalay latex. Any guidance would be helpful.
Hi Bjay0503,
Welcome to the Mattress Forum! 
Yes, you are correct. Dunlop and Talalay aren’t directly comparable in terms of firmness using only ILD numbers because there are several factors that can affect how soft or firm a mattress (or an individual layer) feels besides just the ILD of the material (see post #4 here ) and Dunlop and Talalay that are the same thickness and ILD won’t feel the same in terms of their firmness for most people because they have a different response curve and compression modulus (how quickly a material becomes firmer as you sink into it more deeply). There is more about the difference between Dunlop and Talalay in post #7 here.
Both Dunlop and Talalay latex have their own unique characteristics, with Dunlop “firming up faster” a bit than Talalay (having a higher compression modulus). The use of Talalay in the uppermost layer is quite common, as it does tend to have a bit of a softer feel overall in a similar ILDs as compared to Dunlop, but this is a personal preference. Your overall comfort will of course be determined by the complete componentry within the mattress, as all of the layers work together to create your overall comfort, and nothing can replace your own personal testing.
Phoenix