Hi Ari,
Pressure relief is a very complex subject but in its simplest terms it involves spreading body weight over a larger surface area so that the pressure on any particular part of the body is lower than the pressure inside the capillaries so the blood continues to flow. There’s a very detailed and technical discussion of pressure relief in post #2 here.
As it relates to a material though … pressure relief (and the corresponding sensation of softness) is connected to ILD/IFD, compression modulus, and point elasticity (where memory foam and latex excel and which determines how exactly a material can mirror a certain shape) which along with the thickness of each layer (which is independent of the properties of the material itself) controls how large a surface area is bearing weight and the distribution of the weight. Some types of zoning can also even out pressure by allowing more sinking in of some areas which allows the more recessed areas of the body to bear more weight.
In the case of memory foam it can be even more complex because it’s softness is also affected by temperature, humidity, and the length of time it is continuously compressed so how soft it feels can also depend on the temperature sensitivity of the memory foam and can vary with your environment and circumstances or by how quickly a particular memory foam becomes softer with body heat.
Pressure relief also needs to be balanced with support and alignment because you could use a very thick slab of low ILD and support factor foam to do a great job relieving pressure but the heavier parts would sink in so far that the spine and/or joints would be twisted, bent, or flexed outside of their neutral range this would lead to the pain that goes with misalignment of the spine or joints.
As you can see this is all quite complex but again the three specifications of a foam material that control most of the pressure relief (along with layer thickness) are ILD/IFD, compression modulus, and point elasticity (and temperature sensitivity with memory foam) which together with the thickness of the softer layers create the pressure relieving “cradle” and needs to be balanced against its “opposite” which is support and alignment.
So, the two main functions of every mattress are to keep your spine and joints inside the range of their neutral alignment in all your sleeping positions and to relieve pressure by redistributing your weight across the surface of the mattress (what people commonly refer to as “pressure point relief”.
Because your body is much more curvy than flat and some parts of the body weight more than others (such as the hips/pelvis) and some parts are wider than others (such as the shoulders) … good support/alignment means that parts of your body need to be “allowed” to sink in more deeply and that other parts of your body need to be “stopped” from sinking in too deeply so that the end result is neutral alignment of the spine and joints. Post #6 here uses an example of floating in the air and slowly sinking onto the mattress surface to help you visualize this.
If you were to sleep on your side on the floor for example there would be no support under the waist because most of your weight would be on your hips and shoulders and the middle part of your body would sag onto the floor and your spine would be out of alignment.
In the same way … if you were to sleep on a thick layer of soft foam on the floor then you would certainly sink in far enough to fill in the gaps in the recessed parts of your body but the heavier parts of your body such as your pelvis would sink down too far before they were “stopped” and your pelvis would tilt which also leads to misalignment of the spine. You can see from the diagram here ADMIN NOTE:Removed 404 page link | Archived Footprint: sleeplikeabear.com/files/2689726/uploaded/buyersguide_firmness_guide.jpg
that a mattress that is too soft or a mattress that is too firm can both provide poor support under different parts of the body. There is more about “primary support” (under the heavier parts of the body) and “secondary support” (under the lighter or more recessed parts of the body) and their relationship to pressure relief in post #4 here.
Heavier body types will tend to sink into a mattress more deeply than lighter body types so their concern is that with a softer mattress (with thick/soft comfort layers over the support core) that the heavier parts of his body will sag and sink down too far before being “stopped” by the firmer support core and he will be out of alignment.
People from the “old school” that think “firmer is better” generally tend to choose mattresses that are too firm and they don’t sink in enough to provide good support under the recessed curves of the body or don’t provide good pressure relief (especially for side sleepers).
People that treat mattresses as a “luxury item” rather than a utilitarian purchase that has a very specific function tend to go by “showroom feel” and “subjective comfort” and often tend to choose mattresses that feel great in a showroom but have comfort layers that are too thick and soft or support layers that are too soft to “stop” the heavier parts of the body quickly enough.
Both can lead to uneven support where the spine is out of alignment. The goal is to have comfort layers that are “just enough” and no more in terms of thickness and softness to provide good pressure relief and fill in the gaps in the sleeping profile and support layers that are firm enough to “stop” the heavier parts of the body from sinking down too far.
While all of this might be more information that you desired, it’s a bit of a more detailed way to say that both latex and memory foam can be good options for “pressure point relief”, but it varies by the ILD/IFD of the foam, the combination of materials used in the mattress and their arrangement and thickness, the compression modulus of those foams, the individual sleeping upon the product, their somatotype, their sensitivities and a myriad of other factors. So Big Fig was correct when they told you that pressure point “depends upon the person”, but their overall construction with only one layer of latex in the upper layer would not be as point elastic as a typical memory foam or all-latex mattress or hybrid latex mattress, and it would tend to have a comfort that most individuals would classify as somewhat firm.
Phoenix