Hi JL,
Welcome to the Mattress Forum! :cheer:
While I think you already read it, here is some information about using a solid piece or two piece to approximate the same thickness:
There would be little if any practical difference between two 2" comfort layers and a single 4" comfort layer if they were all the same type and blend of latex and the same ILD (you’re considering 14 ILD talalay) and were inside a tight fitting cover. Two 2" layers would respond a little more independently and because the elasticity of the top 2" wouldn’t be connected and “pulling back” on the bottom 2" when it compresses and “in theory” it may act a little bit softer but in practical and real life terms most people wouldn’t notice any difference in terms of performance or firmness.
Also in “theory only” … two 2" layers that were exactly the same ILD as a single 4" layer could be less durable over the course of a long lifetime because they will act more independently and abrade each other slightly but I don’t think that any difference would be significant or even measurable in “real life” terms and the other factors that affect durability (see post #4 here) such as the firmness of the layers would play a much bigger role. It certainly wouldn’t be a concern of mine.
Multiple layers would have more options for fine tuning though both before and after a purchase. If you found that have tow 14 ILD layers was too soft, you could replace one layer with something a bit firmer feeling. The main advantage of having more layers in other words is that for those who need it, it can provide more options to customize the layer combinations either before a purchase or by rearranging or exchanging layers after a purchase. While this is attractive to some people … it can also add some complexity that may not be necessary or may not justify any extra costs involved in having more layers for others.
Outside of a mattress with more layers having more options to customize the mattress, if a mattress is a good match for you, then one isn’t inherently any better than the other.
The object of the upper layers of a mattress are more for initial comfort, as opposed to “support.” There is more about primary or “deep” support and secondary or “surface” support and their relationship to firmness and pressure relief and the “roles” of different layers in a mattress in post #2 here and in post #4 here that may also be helpful in clarifying the difference between “support” and “pressure relief” and “feel” that may be useful as well.
The theory behind adding graphite to the latex is the increased heat transfer of the graphite, and the benefits that graphite provides to the latex through its anisotropic properties. It is claimed that the graphite adds durability to these softer ILDs of latex. In an overly simplified explanation, the thin graphite “coats” the latex cell structure and is flexible while still imparting strength.
Phoenix