What I believe you are experiencing is phenomenon that is often … mistakenly … referred to as “pushback”. It is part of the most desirable qualities of both latex and HR polyfoam and would also be similar to lying directly on some types of pocket coils. For some however … it is also part of why they don’t like latex. Here’s what I believe is happening.
First of all though for reference … I’ll post your “specs” from an earlier post and the specs of the Nutrition.
[quote]I am 6’3, 210lbs, give or take, by the way. I usually go to sleep on my back, but will sometimes shift to my side during the night. Probably a 70/30 split. I did not buy the topper, by the way. I did not think it was necessary, just “nice”… I’ll wait to see out things go without one first.
2" Natural Talalay Latex 19 ILD
2" Natural Talalay Latex 28 ILD
6" Natural Talalay Latex 36 ILD
1" Support Stabilization latex.[/quote]
With a material that has a high compression modulus (ability to get firmer faster with deeper compression) and a high resilience (ability to store and return energy) … it becomes possible to choose an ILD (tested at 25% compression only) that is softer and provides better pressure relief because as you sink into it it will “catch up” to other foams with a lower compression modulus in terms of its deeper firmness levels and still provide deeper support. This gives materials like this which also have a high “point elasticity” (the ability to compress in a local area without affecting the surrounding area as much) a unique ability to spread out the body weight over the surface of the body and relieve pressure on the more “protuding” parts. They do this by allowing the more protuding parts to sink into the mattress until the wider more recessed parts also begin to bear some of the body weight (are being held up by the higher resilience and compression modulus foam under them). If a polyfoam of the same ILD but lower compression modulus is used on the top of a mattress … then someone who sinks into the mattress to a similar depth will not bear as much weight (have less support) under some areas of the body that are more recessed or flatter.
This ability is why latex, HR foams and similar materials like some pocket springs are so desirable in a mattress and the target for most manufacturers. While they are the “ideal” that most manufacturers strive for, it also comes with a down side … particularly in a mattress where people sink in a little further and the foam under the recessed parts is bearing more of the weight than they are used to with lower quality foam with a lower compression modulus. If you had for example the same ILD’s of lower quality polyfoam in your mattress … more of your weight would be supported by your heavier parts and less of it would be supported by your recessed parts. In particular this affects the lumbar curve and the flatter torso once the shoulders have sunk into the mattress.
In effect … your mattress is allowing you to sink in enough that some parts of your body are bearing weight that are not used to it. For those who need or like this increased support under the lumbar curve … they will call this “support” and if they are comfortable with this … they will feel like they are sleeping in a weightless position or “sleeping on a cloud”. For those who aren’t used to this increased load on parts that have never felt it before … they will call it “pushback” … and for a time it may be uncomfortable. In other words … it is often a side effect of the type of sleeping surface that people are used to and the sensitivity of certain areas of the body to bearing weight.
The reason that “pushback” is not an “accurate” term is because when a body omes to rest on a mattress and the forces are in “equilibrium” the direction of the force is not what is felt … it is the weight being supported along the surface of the body that is felt. This is true with all materials.
So in effect … with the ILD and thickness of the foam in the Nature … you are sinking in a little deeper and while you are likely still in alignment … the pressure has be spread out to areas of your body surface that are not used to it.
So on to what can be done.
The first thing that can be done of course is to re-educate your body to bear weight more evenly and allow the lumbar curve to become accustomed to the increased support. This may take some weeks but if you do adjust to this … you likely won’t want to sleep in any other way after this. Spreading the pressure over a larger surface area really can lead to the feeling of “sleeping weightless” if every area of the body is bearing a load that is below it’s perception of pressure.
The second way is to “lower” the support under the lumbar curve and “increase” the support under the pelvis and shoulders (reducing pressure relief in these areas slightly). This is done by decreasing the amount you are “sinking in” to the mattress as a whole so that the recessed areas are not bearing as much weight.
In the PLB … they use a very elastic and high quality knit ticking which has no quilting in it. This allows you to sink in more deeply into the softer latex and distribute pressure better (bear in mind that for you with a higher weight … 28 ILD still qualifies as “softer”). A thicker layer of wool on the surface will reduce the amount the more “protuding parts” are sinking in and provide some local cushioning at the same time. This will allow the pelvis especially but also the shoulders to “come to rest” at a higher level which means the foam under your lumbar curve will also be less compressed and you will have a little less support (and pressure) in the areas you are not used to being quite so “supported”. This would likely be the “best” fix if your own personal preferences were unable to accommodate the change in pressure distribution of your mattress.
If the ILD’s of the upper layers were either higher or the upper layers were thinner … then this would also likely change the pressure distribution away from the lumbar curves and torso and onto the shoulders and pelvis as well. As long as the pressure on your shoulders and pelvis is below someone’s personal threshhold … then for that person the mattress is pressure relieving.
Part of the reason too that this can happen over the course of a night or several nights is that this increased support may not be felt as uncomfortable over the course of a shorter time frame but become uncomfortable over the course of a night for those who aren’t used to it.
So in essence … Step one is to wait to see if your new “pressure areas” become used to the increased support. I remember when I first slept on latex that I clearly noticed this as well but to me it was not uncomfortable as much as curious. After a few weeks … it was no longer a curiosity but just part of what I liked.
Step two would be to add a topper that had enough softness to cushion local pressure points but help “prevent” the pelvis and shoulders from sinking in quite as far and lowering the weight being supported in these areas. Of course doing this with a wool topper also means that you will also experience the many benefits of wool without it being a part of the mattress itself meaning it can be replaced if necessary without replacing the whole mattress.
I know this is a somewhat “complex” subject and phenomenon to explain as it involves the specs of different materials and why they create a different experience so I hope that this has helped to “demystify” it more than complicate it.