Mattress Forum

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.

Lets say the average body length from a spot a few inches above the knees to the top of the shoulders (where almost all the weight is) is about 36" (I'm about 40"  and 6'5" so probably more than most). I would guess that this included about 85% of the body weight. Lets also say that the "average" width of the body in a side profile is about 12" and that an average weight is about 180 (male). I know these numbers are probably not really accurate but they're close enough for this. This means that this 36" bodylength would weigh about 153 lbs (excluding head and legs from just above the knees to the feet)

This would also mean that the number of square inches in this side profile would be 12 x 36 = 432 (assuming this was all flat which of course it isn't). If every point of this area was being supported equally, then the average pressure would be 153 lbs / 432 sq in = .35 psi.

To qualify as a "pressure reducing support surface", a mattress needs to reduce pressure to below 32 mmHg (also called a Torr) on most bony prominences most of the time. To qualify as a "pressure relieving support surface" it has to reduce pressure to below 32 mmHg (Torr) on all bony prominences all of the time. This is also not quite accurate as fixed numbers like this are not considered to be completely accurate or valid anymore but again for the sake of this post it will do. 32 Torr = .62 psi so if the weight was distributed equally throughout the entire side profile ... there would be no detectable pressure anywhere.

Very low levels of pressure relief (levels below most very sensitive people's detection threshold) would be in the low 20's a good part of the time so lets say 23 Torr or .44 psi

So lets say that 60% of this weight (92lbs) was concentrated in the hips/lower body and 40% (61 lbs) in the shoulders/upper body (of course weight distribution varies here).

Lets say that the hips sank into a mattress' upper layers enough to distribute this weight over an area of 12" x 12" sleeping on the side.

This would mean that there was 92 lbs spread over 144 sq in or .64 psi ... right at the level of pressure relief for most people

If the hips only sank into the upper layers enough to distribute pressure over an area of 6" x 6" (too firm or thin upper layers) it would be 92 lbs spread over 36 sq in or 2.56 psi ... which for many people would equal pain.

If there was enough sinking in in the upper layers to distribute this weight over an area of 12" x 18" (say mid thigh to lower waist) it would be 92 lbs spread over 216 sq in or .43 psi ... which is well below detectable for pretty much everyone.

So all you would have to do in this hypothical case would be to have upper layers just soft and thick enough to let someone sink in just enough that their weight was spread over an area just large enough to bring the pressure to a level below their individual threshhold. This is different for different people. For almost everyone though, a larger 12 x 18 area (upper thigh, hips and some waist/lumbar) would give complete pressure relief. This sinking in can be into a thicker comfort layer or it can use a slightly thinner comfort layer and the top part of the next layer. Either way the pressure relief could be identical.

I know these numbers are not accurate because the body is rounded and doesn't respond exactly to a "formula" but it shows how "sinking in" to a "comforming" (point elastic) upper layer can spread weight over a larger area and relieve pressure to levels below detectable.

The same general idea and "rough math" would apply to the shoulder area.

All of this is also for the most difficult challenge of side sleeping. On the back you would have probably closer to 24" (twice as wide) x 36" surface area which is 864 sq in and if even only half of this surface was supporting all the weight you would have 153 / 432 = .35 psi which would not present a pressure problem for anyone.

The same sinking in that relieves pressure should also offer more gentle support (fill in the gaps) in the waist (on the side) or lumbar (on the back) so this is normally looked after as a "side effect" of dealing with pressure distribution issues. Only people who were completely insensitive to pressure and didn't want to sink in at all (liked sleeping on a floor) would likely have lumbar support issues except in cases where a much higher percentage of their weight was "in the middle" or they were too light and/or thin to sink in enough to "fill in the gaps" in which case other options could be used to create firmer lumbar support (reverse zoning for example).

So if you can create enough sinking in to distribute pressure points over a wide enough surface area using comfort layers (and the upper part of middle layers if necessary) and deal with lumbar support, the only real remaining issues are controlling the depth of additional sinking (non comforming) in the middle and lower parts of the mattress to keep the body in alignment. The amount of sinking in allowed by the upper layers controls pressure relief. The amount of sinking in allowed by lower layers has very little effect on pressure relief (it is not comforming) but does control alignment. This is why when people change the firmness of upper layers to solve support issues they will often create new problems and will often not solve their support issues.

This is where choices come in to use mainly upper layers for conforming pressure relief (softer/thicker with firmer under) or using upper layers and the top part of the middle layers for conforming pressure relief (softer/thinner with slightly less firm under). The first method leads to less (non pressure relieving) sinking in of the heavier "bony prominences" in the deeper layers if necessary for alignment. The second method leads to more (non pressure relieving) sinking in of the heavier "bony prominences" in the deeper layers if necessary for alignment. In either case the pressure relief can be the same, what changes is the alignment that gives the pressure relief.

If all of this can be done on the side for side sleepers, then the much simpler issues involved in back sleeping (mostly stopping hammocking and supporting the lumbar as pressure would rarely be an issue in this position) would be relatively easy to solve using the middle and lower layers.

All of this is because I was curious to see if I could apply some "rough math" to some of what we're doing here and see how close it came. It seems that these examples at least are relatively close to what can actually happen.

Now back to real life (laughing).

Phoenix