Hello Phoenix. I recently (2 weeks) purchased the 1300 from sleep ez. The split layers are S,M,F,EF. All natural talalay. My question is: what is the thought process as far as the effect of a soft layer under a firm layer? Soft on top has not worked well for us. Right now my side is M,S,F,EF. Her side is F,S,M,EF. At first this seemed good but now still too soft. Are the softer layers “wasted” underneath? Thinking about swapping the S’s for M’s. She is a side, stomach sleeper. I’m all three. Both have slight back pain in the morning. Although nowhere near as bad as with the old spring mattress.
Hi roofer21,
Good question 
As a general rule … the closer to the top a layer is the more effect it will have on the pressure relieving qualities of a mattress. The lower in a mattress a layer is … the more it will affect the support qualities of a mattress.
In addition to this … layer thickness (and mattress thickness) also plays a role with this. Thicker layers (and mattresses) act softer because they don’t get as firm as quickly (foam gets firmer according to the percentage of it’s height it’s compressed). This means that thicker layers or mattresses can use firmer foam and feel softer than thinner layers or mattresses which gives a greater range of compression before it gets so firm that it feels like it’s bottoming out. This is particularly useful with heavier weights or larger body sizes where a greater range of compression is needed. Thickness and firmness in other words act together.
In addition to this … pressure on top of a mattress moves downwards in a cone shape meaning that surface area of the pressure on top is spread out over a larger area the further down you go (meaning that a soft foam on top will compress more than a soft foam lower down because the weight on it is more “concentrated”).
So the effect of having a softer foam under a firmer foam is that the pressure relief potential of the softer foam is reduced (it doesn’t contribute to the depth of cradle as much) while at the same time the supportive abilities of the foam are also reduced (it doesn’t hold up the heavier parts and keep the spine in alignment as well).
Of course if the pressure relief and support of this type of layering is optimal for a particularly individual … then nothing says that it would be bad … but it certainly doesn’t take advantage of the natural progressive resistance abilities of latex nearly as much and it would be much more difficult to find the best combination and balance of pressure relief and support.
If for example if a Medium top layer worked well for pressure relief … then it is usually better to put firmer foam underneath this to keep the spine more aligned. Softer foam underneath would “add” more to the pressure relieving properties of a firmer top layer than firmer foam under the same layer but if the pressure relief was already good enough … then it could cause alignment issues by allowing the heavier parts to sink in too far.
The goal with pressure relief is “just enough” in terms of softness and firmness and “as much as possible” for support layers which can help the comfort layers adjust to different sleeping positions and profiles and different weight distributions over the course of the night.
So “soft” is relative to whether someone is referring to pressure relief or support and with each of these … soft or firm means very different things. A mattress needs to be both “soft enough” on top for the best pressure relief for each individual and “firm enough” in the support layers to keep everything aligned in all sleeping positions.
So while the softer layers are not “wasted” … it seems clear that they are not contributing to the overall balance of the mattress nearly as much as they could be.
I suspect that the soft on top was not so much a pressure relief “soft” problem but more of an alignment “soft” problem. Fixing “pressure relief” too soft (in any of the layers) with changes that lead to less pressure relief and also less support can create a lot of confusion and frustration. The key is to separate out the two different meanings of the word “soft” and relate them to pressure relief and alignment and then make changes which correct the one (or even both) that are not optimal.
While I don’t know your height weight or sleeping positions which of course would make a big difference … if Medium provides good pressure relief … then I would go firmer underneath as that will also increase the odds that the alignment will be better as well (and the overall mattress won’t be as likely to feel “too soft” no matter what is on top)
I know that this would cause some looseness in the cover but it may be worth trying M/F/XF (3 layers) to see how this works or even S/M/XF as both of these would be softer on top but much firmer in terms of support. Very few people would be comfortable with a F layer in the top of a mattress unless they were back or stomach sleepers and even then it may be a little too firm. I strongly suspect that with the 4 layers you have in addition to the ILD of the layers that the “softness” you are referring to is more about how far you are sinking into the mattress as a whole rather than the softness of the comfort layer and pending your further feedback … it’s the “firmness” of the support I would be looking at.
Phoenix