Mattress Forum

A bit of background first ... hope that's OK.

If you have a piece of foam with an ILD of say 20 and a high sag factor of say 3 (like latex) then it only takes 20 lbs to sink in 25% but it would take 60 lbs to sink in 65%. To go past this would feel like you are laying on a board. This means that you don't really go "through" the layer so much as reach the point where the compression won't go any further based on the body weight on top of it. How much sinking in there is along your body at this point (where no part of you can compress the layer any more) determines how well the pressure is relieved. The idea is to sink in to a layer enough so that the lighter and more recessed areas of the body are also taking up the load. This distributes pressure and relieves pressure issues.

If this 20 ILD layer was on top of a 44 ILD layer, then the 44 layer would actually be much softer than the compressed 20 layer in the first inch or so. It would start to compress long before the top layer reached 65%. When a really firm layer is only compressed a little bit (say 15%) then it will actually be much softer than it's ILD. This is why even a 44 ILD layer under a thicker softer one can still feel very soft at he very top of it's compression range.

The advantage of having a much higher ILD under a much softer one is that if the softer one only lets you "go through" a litle bit, then the upper part of the firm layer underneath will be soft enouth to allow enough sinking in to "finish" the pressure relief. Because it gets firmer more quickly with compression, it will also not allow enough sinking in of the heavier parts to cause alignment issues. The "critical zone" is really about knowing the thickness of the upper layers that are needed before it gets firmer than the support layers underneath and the softer part of the firmer layers "take over" the last part of pressure relief.

So on to your experiment: (I'm going to call the soft talalay 3" and the convo 1.5")

On my side I could feel my hips bottom out and start to ache pretty quickly (which is different - normally my shoulders ache).

This tells me that it is likely that 3 + 1.5 of soft talalay is likely enough to relieve pressure. If it was too little you would actually "hurt" rather than "ache" on a floor. Even 4" may be enough with the "softer" part of a firmer layer underneath.

On my back it felt like my butt was hitting bottom, and felt weird on my back, but I didn't stay long enough to start hurting.

On your back you would likely feel like your butt was "hitting bottom" because it was the only part of you that was really compressing the layer as your upper back has a flatter wider profile so the feeling of "hitting botttom" with your rear end would be expected. There is really only one part of you compressing (butt) rather than 2 on your side (hips and shoulders). The "wierdness" on your back was probably because your rear or hips were sinking in enough and then "being stopped" that the lumbar was taking up more of the load. Depending on what you mean by "wierd" it may actually be a good thing.

When you added the second 3" layer it shouldn't feel that much different in theory (which it didn't) because in both cases you have a thickness that is already more than your critical zone. It wouldn't "stop you dead" though underneath so the feeling on your butt would be less. Where it would make a difference is in how far it let you sink to get similar pressure relief.

With the 3+3+1.5, the pressure relief would have been slightly better (the bottom 3" would be "Finishing the job" instead of the floor") but my expectation would be that it is a lot too thick and would cause you a sore back and misalignment over time.

My guess is similar to what I thought at he beginning which is that your "critical zone" is about 4-4.5" and that along with the "soft upper part" of a much firmer base layer would both give you pressure relief and keep you in alignment. You need this much of soft to allow the presure relief to happen with both your hips and shoulders. The 4.5" in combination with a much firmer next layer may be just right or it may be a little too thick. It would depend on the ILD of the next layer. With a "progressive" next layer it would likely be too thick (a 28 or so would feel softer but allow too much sinking in of your hips) but with a firmer next layer it would be pretty close (you would only be using the very soft top part of the firm ... say 40 ILD layer before it "stopped" you).

So my guess would be to put the Convo over the 3" soft Talalay and then test out which next layer allows the softness you need (probably any of them) and gives you the best alignment (maybe none of them). I would think that the firmer the better to start with (Dunlop firm side up would seem to give the best odds). The danger here is that a softer layer under the firmer Dunlop one may allow you to sink too far. This is why I was hoping for the 4.5 inches over the Dunlop by itself as the bed base would be the next best thing to a 44 or Xfirm bottom layer which I suspect would be best.

There is a possibility that 1.5 convo over 3" soft over 3" soft would work (alignment with a deeper "cradle") but with a medium under this I would really think you will sink too far with your hips and go out of alignment. This may only work with a really firm support layer and even then it would likely be too thick for a comfort layer.

So my dilemna now (after you've tried out your soft convo + soft talalay + soft talalay experiment) is what to put under 1.5 convo + 3" soft talalay + 3" medium dunlop (which may or may not be firm enough). It seems that anything "left over" after that would be too soft to keep you in alignment.

Depending on what happened, the medium talalay instead of the med Dunlop may be better (if I've really underestimated your critical zone or for better shoulder pressure relief) but I really do suspect they may both be too soft.

If only we had a 40 or 44. The next best thing to stop a deeper layer from sinking in too much is to put a thin firm layer over it (cardboard?) if you want to "fill up" your case.

Let me know what happens with your setup tonight as we can learn from every combination.

Phoenix

Regarding my current situation, I do have 2 medium dunlops and can use of them (wife can sleep on almost anything). So maybe I should try them under the soft talalay + the conv foam? I won't try this tonight as I want to try the "soft" setup (altho I suspect it may be too soft and hurt my back)...

Steve

PS - are you like a foam engineer? how do you know so much about this stuff?

Dunlop has a steeper "curve" than talalay which is why it feels firmer. The very top 25% may be the same but because the deeper part of a Dunlop layer is denser ... and because most people sink in more than 25% ... it feels much firmer with "average" (more than 25%) compression. The transition from soft to firm is faster because the top of the dunlop is as soft as it gets while talalay is more consistent all the way through in terms of density. A 3" 20 ILD Dunlop would act more like a 1.5" 20 ILD Talalay over a 1.5" 28 ILD Talalay for example. One isn't any better, just different.

I would certainly try the 2 Dunlops under the Talalay and see how that goes (after your "soft" experiment). I would use them both with the firmer side up and hope that the weight of the layers would slightly compress their "softer" side and "firm them up a bit". Then you would have the option of using the middle dunlop softer side up it you needed to "finish" the pressure relief more using the middle layer. It may even be that 3" soft talalay over medium Dunlop soft side up would just do it but I would think this would be a close call and you'd be "safer" with the topper. If you need it (and these are small changes) and are ok with the feeling, the bumpy side of the topper up may also let you sink in a bit more with your shoulders without really affecting the depth of your hips.

As an example, if you needed say 4" of "sinking in" in a part of your body to get enough pressure distribution along your body profile to relieve pressure past your "discomfort level", and the upper 4.5" layers gave you say 3" of that before it became "too firm", then all you would need is enough softness in the first 1" of the next layer to get the pressure relief you need. This is where dunlop may excel in some cases because it would give you the soft upper section and then become firmer faster.

Balancing the shoulders and the hips for alignment can be tricky as the shoulders have less weight (about 1/3 of your body weight) than your hips (almost half of your body weight) but typically need to sink in more for side sleepers. Usually more so for men than women who usually have wider hips. How far your shoulders need to sink in on your side depends on how much you sleep on shoulder/upper arm (lower hand under your head is an example) or on your shoulder/ribcage on the side (lower arm more forward). The "ribcage" sleeping will balance the load on your shoulders with less compression than shoulders/upper arms (which needs more sinking in to get to the ribcage). Until you get to the ribcage, the shoulders have less surface area so sink in more easily, once you get to the ribcage, there is more surface area so it tends not to sink in as much. The "surface area" in other words of the heavier parts makes a difference in how much they sink in and how difficult it is to control the depth that gives pressure relief and also keeps each part of the body in alignment. Pillows also of course affect the depth the shoulders sink in, how much weight they hold, and spinal alignment.

Sometimes a really soft and thicker upper layer over really firm is a good way to go for more "difficult" cases. This lets the shoulders sink in enough to get to the ribcage and relieve pressure and will also keep the hips with their larger surface area from sinking in too far to hammock. The hammocking is usually from too soft mid and lower layers ... but sometimes from too thick comfort layers.

It's funny but sometimes a single ILD layer could actually offer better pressure relief and alignment because of it's "progressive firmness" than multiple layers, particularly in back or stomach sleeping.

It's kind of fun to try and "visualize" what may be happening, especially when you can't see it first hand, and I guess that's the "intuitive" part of it as opposed to the "theoretical" part of it. Sometimes even the words people use (like the difference between "hurt" and "ache") can give clues to what's going on.

Anyhow I've probably rambled enough (again :)) but hopefully this will give enough options to really make a difference.

Phoenix

PS: I'm not a "foam engineer" but for some reason I do find all this really interesting. Maybe I just love sleeping (laughing).

Steve

All Dunlop including Sleepez's has this characteristic (the latex settles a bit) ... some more and some less depending on their method of making it and the types of pins they use. I checked with Shawn at Sleepez to see if he had a better way to tell but he agreed that if your piece had a label that it would be the easiest way. I'm apparently the first one who ever asked him :).

Phoenix

Phoenix

The labels are on top or bottom (not on the side) So the label side is the soft side?

And you want me to setup my mattress:

• convo foam (flat side up)
• soft talalay (label up or down?)
• med dunlop (label down)
• med dunlop (label down)

Just checking. Also should I change my wife's side to put the labels down?

By the way, last night's config caused more back problems, definitely not enough support...

Thanks for the feedback on last night. I guess the "soft" experiment is helping to confirm our direction.

As far as your wife, I guess it would depend on how she felt about what she has now. I would be tempted to change it to the same as you just to see if she felt any difference as well. You said she could sleep on anything but she may find she likes one or the other better.

Happy sleeping! :)

Phoenix

Phoenix

PS: If you can tell a difference between the two dunlops as well, I would put the firmest one in the middle (closest to you). Result may be marginally better.