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Constructing an HR foam mattress 22 Jan 2012 21:09 #1

Hi Phoenix,

We plan on constructing a mattress of HR foam (3 lb density, 2.5 support factor).

This will be a blind construction (ordering online), not having tested mattresses, and trying to make decisions based on the info in all the articles on this site. The site is very informative (amazing, really), but without having had opportunity to experience the HR foam, we're not sure how to apply the general construction advice to our own statistics and sleep positions.

To help us get as close to correct on the first try, I have some questions.

First our sleeping positions, and height/weight:

Side/back sleeper: 5'11" 150 lbs
Side/back sleeper: 5'2"
Both with average shoulder and hip widths.

Is a differential mattress construction to be absolutely avoided for side/back sleepers?

The Sleeping Positions article indicated that "Higher quality materials that become increasingly firm at a faster rate with deeper compression can also eliminate the need for a middle or transition layer."

Might the quality of HR we are considering work for us in a differential construction, or might we better guess that a progressive construction would work best for us?

Based on our height/weight and choice of HR foam, would you be able to offer some guesses at ILD's, and thickness of layers that might be a good starting point for us to begin our experiment?

As an aside, we'll make a mattress with one half optimized for me, and the other half optimized for my wife. We'll begin by purchasing the materials for one half. This way we can guess at thickness and ILD and number of layers, test it, and then better choose what to order for the second half, as well as to better know how to adjust the first half if necessary.

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Re: Constructing an HR foam mattress 22 Jan 2012 23:08 #2

Hi DanielH,

This should be an interesting project :)

Your height and weight certainly help (lower weights than average) but it would also help to know a little bit more about the types of mattresses in general that you have been most comfortable with to get a sense of your preferences as well. Do you like sinking in more deeply, do you like firmer (more on top of the mattress), do you tend towards pressure issues, do you have back issues. All of these and other guidelines from your history would help to narrow down the "best" theoretical construction for you.

Is a differential mattress construction to be absolutely avoided for side/back sleepers?


What I have called "differential" and "progressive" constructions are really different pathways to the same end which is good pressure relief and alignment. The differences between them don't have clearly defined "edges" but are more of a general approach to layering.

Each person needs a pressure relieving cradle which is deep enough and conforms to their body shape enough to relieve pressure points below their pressure tolerance. Lets say for the sake of argument that this cradle needs to be 3". This would mean that a 3" comfort layer that was soft enough to provide most of this pressure relieving cradle could use a much firmer support layer below it. A comfort layer that was only 2" in this case wouldn't by itself provide a deep enough cradle and if the layer below it was too firm you would "go through" the top layer and your pressure points would be supporting too much weight on too small an area because of the firmer layer below it. While all the layers of a mattress compress simultaneously ... it helps to visualize this to think of the layers compressing in a certain order (first the top, then the next etc). In a case like this ... you would use a softer support layer to help form a deeper cradle. If the comfort layer was already soft and thick enough ... then it wouldn't need any help and the support layers could be as firm as you needed them to be for best alignment.

Typically a comfort layer will come in about 1" increments which means that in most cases you need to choose between 2" and 3". Adjusting middle or lower layers however can create finer adjustments. This is where the support factor comes in.

If you had 2" of 20 ILD foam on the top of a mattress and you needed an extra 1/2" of cradle then a 32 ILD layer (which needed 32 lbs to compress a 4" layer by 1") would only need less than 16 lbs to compress to 1/2". It would then take @ 46 lbs (30 + 16) to compress a further 1" (1.5" total). What this means is that a 2" layer of 20 ILD over 32 ILD foam would give you the depth of cradle you needed but beyond this it would be roughly as supportive as a 46 ILD support layer. This would be the very rough equivalent of 2.5" of the same type of comfort layer over 46 ILD foam. The first example would be more progressive and the second would be more differential but would end up with roughly the same pressure relief. Of course the math here is not exact but the idea is that they would be roughly equivalent.

Another way to put this would be to use a 4" layer of 15 ILD polyfoam with a 2.5 sag factor as an example. This foam would take 15 lbs of pressure for a 50 sq inch foot to compress it by 1". It would take 2.5 x 15 or 37.5 lbs to compress it by 65% (roughly 2.6"). This means that it would take an extra 22.5 lbs to compress it the extra 1.6". So this foam would take a little more than 7 lbs to compress 1/2" (compression curves are not usually linear and the initial compression curve is generally steeper than the subsequent compression curve with deeper compression), 15 lbs to compress 1", 22 lbs to compress 1.5", 29 lbs to compress 2", 36 lbs to compress 2.5" (the middle range of compression is more linear) and about 45-50 lbs to compress 3" (the deepest compression is also not linear and starts getting firmer even faster which could be called bottoming out). This means that an area around the hips that was exerting 50 lbs per 50 sq inches of pressure could compress the top 15 ILD layer 3" but a 50 ILD lower support layer by only an extra 1". The odds are good that by the time you have sunk into the mattress this deeply that the surface area of your body that was bearing weight would be less than 50 lbs per 50 sq inches. Of course the process of how each layer reacts is along a continuous spectrum rather than in "steps" as in this example and is further influenced by the thickness of the mattress as a whole but the idea is correct.

The reason that differential is "easier" but progressive can be "more accurate" is because differential allows you to choose each layer more for a single purpose (either pressure relief or support) without taking into consideration as much how they interact or influence each other. You can choose a top layer that you know is thick and soft enough for good pressure relief without worrying as much about whether you will feel a really firm support layer underneath it. The advantage of the progressive is that you can fine tune the layering more (you're not limited by the thickness increments of the comfort layer materials). It can also use thinner comfort layers which can often allow the support layers to provide better support for multiple sleeping positions.

One other thing to bear in mind is that latex is usually tested for ILD with a 6" layer while polyfoam is tested for ILD with a 4" layer which means that the measurements don't directly translate into each other. ILD taken with a thicker layer needs more pressure to compress it 25% because the 25% thickness is more than with a thinner layer. The net effect of this is that latex ILD's will be slightly softer than the same ILD's in polyfoam.

Having said all that (and I know that this can get quite complex) you have the benefit or working with a HR foam with a higher sag factor which means that you have more flexibility when it comes to choosing layers.

Subject to knowing your "history" and "preferences" ... I would tend to start off in one of two directions depending on how "risky" you wish to be.

The first (differential) would use a 3" comfort layer which because of your lower weights and with the right firmness should give you enough thickness that you can choose a firmer support layer below it without worrying about feeling it. I would likely choose an ILD in the range of 15 - 20 (which would be a little firmer than latex in the same ILD). Under this I would put a firm 6" layer in the range of high 30's or low 40's. To save money you could also use HD foam in the support layer although HR would work a little better (because it's support factor would be higher and it would "hold up" your heavier parts better). Average ILD (assuming 15 ILD top and 40 ILD bottom) would be @32

The second approach would use the same ILD foam in the top layer but it would be thinner say 2". I would put this over a 3" "transition" layer in the high 20's to low 30's (to give you a deeper cradle but also better support once you reached the depth of cradle you needed) and then a lower layer of another 4" or so of very firm (@ 48). Average ILD (assuming 15 over 28 over 48) would be @ 34.

The unknown about either of these would be your "critical zone" which is the effective depth of cradle that is best for you and that provides enough pressure relief for your sensitivity and of course your preferences and YMMV.

Phoenix
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Last edit: by phoenix.

Re: Constructing an HR foam mattress 23 Jan 2012 02:01 #3

It's like drinking from a fire hose. :)

I forgot to add my wife's weight: 120 lbs

Our source for foam allows for 1/2" increments, which may help, or just be yet another choice to deal with :)

My wife's favorite mattress was one she slept on one summer several years ago. She described it as soft on top, and then firm underneath. Her recollection is the top soft layer was 2" or so. At the time she often had back pain, and this mattress helped it out a lot. Whether or not there were more than two layers she doesn't know, and doesn't know what materials were used. She tends to like a more on top of the mattress feel, not sinking down into it deeply. Pressure on her hip from a firm-only surface, like the floor, is very uncomfortable for her.

Lately she's been waking with mid to low back pain, but we've been on a futon mattress, probably some kind of awful, sagging, fiber filling. Anything will be better. :) Her current back pain appears directly related to our sagging, unsupportive mattress.

For me, I can't say any mattress type I've slept on stands out in my mind as best, just one that doesn't sag and isn't too firm. My sense of what I'd like is to be able to "sink in" just enough to fill in the gaps. I'm not looking to melt into a pillowy cloud, so probably more of an on top of the mattress feel for me too. No back or pressure issues for me.

In the differential scenario (with a 3" comfort layer) a 6" core sounds deep. Why is this more supportive than say a 3" or 4" firm core?

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Re: Constructing an HR foam mattress 23 Jan 2012 18:44 #4

Hi Daniel,

It's like drinking from a fire hose.


Yeah I do that sometimes ... but I just couldn't resist the temptation. Your questions were just too good :)

I guess the short version could have been "go thicker over firmer or a little thinner over slightly less firm" but it wouldn't have been nearly as much fun answering you.

In the differential scenario (with a 3" comfort layer) a 6" core sounds deep. Why is this more supportive than say a 3" or 4" firm core?


A thinner support core would actually act firmer so in a sense it would actually be more supportive. It would compress to a greater percentage of its thickness and get firmer much more quickly so it would have a much lower and less gradual "range" of compression. Every layer of a mattress compresses with pressure and contributes to pressure relief but the deeper a layer is the less it will compress with pressure on the top (the pressure is spread out over a wider area in the lower layers). What this means is that the support layers play a secondary role in helping a mattress to adapt to different sleeping positions and if this layer is too thin ... it can't adapt as well to either different body profiles that come from different sleeping positions or absorb the "shock" of movement as well without feeling like you are "bottoming out". So if someone was purely a back sleeper for example a thinner support core may work well but with movement or with a change of sleeping position it wouldn't adapt as well to the new body profile or cushion movement as well. The effect of this would be different for different body weights, body shapes, and sleeping positions. The bottom line is that a thinner lower layer may work well for certain people but it would be "risky" for most.

I have to ask is there a reason you haven't tested a few mattresses to get a rough "real life" reference point for layer thickness and softness that you prefer? There are so many variables that it's somewhat difficult to know exactly how someone will react to specific layer thicknesses or softness without one ... but since I've gone this far I'll share what I would be thinking if I was in your shoes.

With your wife's weight, back issues, and combination sleeping I'd tend to go a little softer and thinner on top than what would be "typical" for a side sleeper so since you have the option of 1/2" increments I'd probably go with 2 - 2.5". I would put this over a fairly firm (for her) support layer in the range of 36 ILD or even a little higher. Thinner would be a little better for back support but if it was too thin then she may not be isolated enough from the firmer layer underneath and feel pressure on her side so my tendency would be to go in between what is typical for a back and side sleeper. Here is where a thicker support layer would also help more because it would help to better adapt to different sleeping positions. The goal here is a more differential construction where there is a "soft over firm" feeling which she seems to like. The firmer support core will help with alignment and the back issues. The goal would be to have the comfort layer "as thin as possible" as long as it provided good pressure relief. I doubt I would use a support core that was less than about 5" and 6" would be more typical.

You would also likely do well with something similar because you are heavier but your weight is also spread out over a longer body. With most women the challenge is to "stop" the heavier and wider hips from sinking in too far (thus the firmness underneath and the tendency towards a thinner comfort layer) but with most men the challenge is to "allow" their wider (and lighter compared to the hips) shoulders to sink in far enough. Side sleeping here would normally use around 3" of softer foam making sure it wasn't so firm or thin that the shoulders couldn't sink in far enough to spread some weight onto the torso and relieve pressure. Again though because of your preference towards a more "on" the mattress feeling and your lighter weight ... 2.5" may work well (more so with a slightly thicker support core) and would be better for your back sleeping as well. I would also use the same support layers because it will "act" a little softer for you than it would for your wife and you may need a little extra softness for your shoulders with a 2.5" layer.

So since you are starting with one side ... I'd start with something like this and then use it as a reference point to decide on any changes needed for the other side. You may even end up "taking" this side for yourself and making adjustments the other way around :)

It's pretty "risky" to make suggestions without any reference points so as long as you take this as more general ideas and design concepts rather than specific recommendations then hopefully it will help.

Phoenix
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Last edit: by phoenix.

Re: Constructing an HR foam mattress 24 Jan 2012 01:33 #5

I much prefer the fire hose version over the ten peso version. :)

I see now why the thicker support layer would be preferable. I do understand that I shouldn't consider this hard and fast advice, and greatly appreciate your thoughts/recommendations specific to us. Even though I feel I have pretty well understand the information from this site in an abstract way, I wasn't fully confident how to approach this project not having direct experience with ILD firmnesses. I find I had been thinking on the same basic design lines as you suggest, but you've really helped me to understand the importance of base thickness as well as which ILD's might be a good place to start.

As for why we have not tested mattresses, it's mainly due to being in a rural area, which doesn't offer many choices for mattress testing. Secondly I haven't been confident I'd find a mattress constructed much like what we're looking for as far as an all HR foam construction. Admittedly I have only briefly searched, and really should search some more for a store not too distant that may offer a chance for first hand experience.

I'll look some more for stores not too far away, but even if I don't find a place, my new found knowledge from you has me (over?) confident this little experiment can be pulled off with few or no hitches. And, besides, whatever mattress we get would be much better than what we now have.

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Re: Constructing an HR foam mattress 24 Jan 2012 03:01 #6

Hi Daniel,

It can be a really enjoyable challenge to "design" a mattress that is a little different from the norm (which on this forum is usually latex or memory foam) and there is a sense of satisfaction in sleeping on something that you created from the ground up.

I think you have good reason to be somewhat confident and I think you are approaching this project with a great plan. As long as the polyfoam you are buying really is high quality (and based on your posts you seem very clear how to tell the difference and the importance of knowing what you are buying) you are using materials that can result in a very good mattress at a lower cost than materials such as latex.

While you may not have anything close to you ... if you let me know your zip I can certainly take a look to see if I know of anything that may be reasonably close by that would be worth including in any testing.

Phoenix
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Re: Constructing an HR foam mattress 25 Jan 2012 21:30 #7

Actually, in my internet search you again were most helpful, as you responded to someone looking for a store in vicinity I would need to look. The following post on this forum leaves me thinking my best bet may be Bountiful Rest Mattress Company:

www.themattressunderground.com/mattress-forum/general-mattresses/584-local-mattress-manufacturers-in-provoslc-ut.html

If I can soon make a trip to them or one of their retail outlets I may test out what they have in latex that may compare to what I'm considering for HR foam. I realize it would be a different feel, but it should give a more sure idea of what I'll want in ILD's. But if I can't get there soon, I may just take the risk on my plan to build blindly.

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Re: Constructing an HR foam mattress 26 Jan 2012 03:44 #8

Hi Daniel,

That sounds good. He was very helpful when I talked with him on the phone. They use talalay as well which would be closer to HR poly than Dunlop. Just bear in mind that the ILD's don't translate exactly and that latex would be about 20% less if it was tested on a 4" layer like polyfoam instead of a 6" layer (24 ILD @25% compression on a 6" layer would be about 19 ILD @25% compression on a 4" layer).

Phoenix
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Re: Constructing an HR foam mattress 14 Feb 2012 03:18 #9

Okay, we went with the blind foam order, not testing mattresses beforehand. We ordered one half of a mattress, comprising a 2" comfort layer, and a 5" support layer. Works perfectly for my wife. She looooves it. But my hips/butt sink down too much into the support layer, or you could say my shoulders/back don't sink down enough. Whether on my back or on my side, that's how it felt as I (fitfully) slept on it, and we took photos from the side that confirm this.

I see two options, but maybe you could point out more. One, hit the gym and bulk up my upper body. Heavier upper body sinks in more, giving better alignment. :) Two, zone my support layer, either choosing a softer support layer in the area under my upper body, or choose a firmer support layer in the area under my hips. I am, however, concerned that zoning may create complications as far as keeping my body aligned to the mattress. But I don't know.

I did consider the idea of simply choosing to make the entire support layer firmer (no zoning), but it seems to me it may have the same effect, with my lighter shoulders/back sinking in less than my heavier hips/butt. But, maybe not the same effect, as my experience with sleeping on firmer surfaces hasn't provided the same of out-of-alignment.

What are your thoughts?

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Re: Constructing an HR foam mattress 14 Feb 2012 03:50 #10

I just read over your zoning article, and the third option is sounding like it may fit me best. My hips are fairly narrow in relation to my shoulders. My lumbar region when I lay on my back definitely wasn't well supported - I checked for this by slipping my hands behind my lower back, and there was a gap. However, I didn't check for a gap when I lay on my side. And in looking again at the photos we took as I lay on my side and back, it looks more like my shoulders and back are supported too high, and less like my hips are sinking in too far. This is getting complicated.

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Last edit: by DanielH. Reason: misspelled word: lumber to lumbar
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