Hi CCoffey,
There is more about the different ways that one mattress can “match” or “approximate” another one in post #9 here but there are hundreds of different types of memory foam formulations made by many foam manufacturers that can each have very different firmness levels or properties from each other even if they are exactly the same density (see post #9 here and post #8 here) so it’s not possible to predict how a mattress will feel based on knowing the density of the memory foam or based on the specs of any of the individual layers because there are too many different versions of memory foam in every density and there are too many variables to take into account that can affect the feel and performance of a mattress “as a whole”.
Because of all the variables involved … the only way to know for certain how all the layers and components interact together with any particular person and how a mattress will feel for you or how closely it will “match” another mattress in terms of PPP with any certainty is based on your own personal experience when you either test it in person or sleep on it.
I would keep in mind that while the Casper mattress has a thin layer of latex in its design … it’s only 1.5" so it’s not really a latex mattress or even a latex hybrid because the “feel” of the comfort layers would be a combination of the feel of synthetic latex and the 1.5" of 4 lb memory foam that is underneath it in combination with the smaller effect of the “feel” of the polyfoam support layers underneath both so testing a latex or a latex hybrid mattress that doesn’t include memory foam may not be very comparable. Even a mattress that used the top two layers in the reverse order but was otherwise the same would feel very different. I would also keep in mind that the actual thickness of the individual comfort layers isn’t all that determines the depth of the pressure relieving cradle in a mattress and it isn’t as important as how the mattress feels and responds “as a whole” in terms of PPP. Again … every layer of a mattress will have some effect on the layers above and below it so even changing the firmness of a support core under 3" of comfort layers would make a difference in how the mattress feels in terms of pressure relief and support. For some people (particularly in higher weight ranges) the compression of upper part of the deeper and firmer base layer would effectively become part of the “comfort layers” even though it’s not a separate layer by itself (see post #2 here).
Specs are great to help identify any weak links in a mattress but they are not a good way to predict how a mattress will feel or perform for any specific person and even the most experienced mattress designers that are very familiar with a very wide range of different materials and combinations of materials will often be surprised at how a mattress “feels” in real life compared to how they thought it would feel based on specs or “theory”.
Local testing can tell you more about the general “feel” of different types of latex compared to other types of latex or compared to other materials such as memory foam so you can decide on which materials or combinations you tend to prefer in general terms but there are so many versions of each type of material and so many different mattress designs in each mattress category that even though local testing would give you a good sense of the general characteristics of different materials and combinations … it may not tell you much about how a specific mattress will feel unless a mattress you test is close to identical with another mattress you are considering in their design and the thickness, type, and firmness levels of all the layers and components inside it (including the cover) which isn’t very likely or someone that is familiar with both (such as a manufacturer or retailer that you are considering) can tell you how they compare “as a whole” based on their personal experience.
Once you are down to finalists that are between “good and good” and there are no weak links in any of them and no clear winners between them … then any of them would probably make a suitable choice and your final choice (see post #2 here) will really be a matter of “informed best judgement” based on your testing experiences or conversations with each of them along with all the objective, subjective, and intangible parts of your personal value equation that are most important to you.
Phoenix