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Putting the layers together - Differential construction

The common factor in all differential constructions is that they use a comfort layer that is THICKER than the recessed areas or "gaps" in a sleeping profile. If for example you need a pressure relieving cradle that is 3" deep (average side sleeper), then a differential construction could have a comfort layer that was at least 3" thick and usually a little more. In this type of construction, the comfort layer is designed to do all the work of forming a pressure relieving cradle and supporting the recessed lumbar area and the support layers below it are only used to keep the spine in alignment by preventing any further sinking down by the heavier parts of the body. This means that in this construction, a comfort layer needs to have all the qualities that are necessary by itself as it does not “borrow” qualities from the layer below it. This means that for pressure relief, it needs enough softness and point elasticity, and for lumbar support it needs a higher sag factor and resiliency. In other words, if you needed a 3” cradle for good pressure relief then you would use a comfort layer that was about 3” - 3.5” thick.  If you needed a 2” cradle for pressure relief, then you would likely choose a comfort layer that was 2” – 2.5” thick. The comfort layer would always be at least as thick as the cradle that you need and usually a little thicker.

 

Advantages:

Differential constructions are much more simple than progressive since they use the qualities of a single layer rather than combinations. Since there are so many high quality materials available that are good in all the areas required for a comfort layer, it is simply a matter of choosing an appropriate thickness and ILD and thickness of a high quality material. The other qualities that are needed (point elasticity, sag factor, and resilience are already a side effect of this choice. In this case, latex, HR polyfoam, and microcoils which all have versions that have lower ILD, high sag factor, high resilience, and good point elasticity that are necessary in a good comfort layer. In some cases collapsible column gel may also make a good choice here since it also has the “built in” ability to support the lumbar (with the stiffer columns that have not collapsed) but may not be available in a thick enough layer in which case it would need a progressive construction. Because the comfort layer is based on a single material over a firm support layer, it is much easier to “get it right” than the more complex progressive approach.

They can use a much wider variety of support layers, including lower cost materials, because the main quality of a support layer that is needed in this type of construction is firmness to control the sinking down of the heavier parts of the body and any support layer can be made in a firm version.

In a 3 layer mattress, it becomes much easier to choose the middle layer (part of the support core) as it only needs to be similar in firmness to the bottom layer so the overall support core is “firm”.

 

Disadvantages:

This type of construction depends on the use of comfort layers that are higher quality and have many qualities so the choices of material in the comfort layer is more restricted. It is also important to remember that there are some materials that can feel very good and have many of these qualities such as softness, point elasticity, and resilience at a lower level and for a short time (such as lower grade polyfoam) . While these may feel good in the store and for a short time afterwards, they will quickly lose their qualities and good dreams may turn into nightmares. In a differential comfort layer that feels good when you are testing it, knowing what it is made of and it’s expected durability becomes very important.

This type of construction should not be used at all with certain comfort layers such as natural fibers and should be used with real care if at all with others that have weaknesses in certain areas such as memory foam where they are usually only used in certain cases (such as those few with thin very evenly distributed body profiles that do not require the same degree of targeted lumbar support and do not have a tendency to sink down too far in certain areas of their body but still need good pressure relief overall).

Overall, this would be the preferred construction method for those who wish to simplify their mattress shopping or those who are buying a mattress without lying on it first. It is much easier to predict what a mattress of this type will feel like based on what other mattresses with similar constructions and layer thickness feel like in the stores. In other words, a mattress with this type of construction can be more easily duplicated with other materials and through other suppliers which opens up great possibilities for greater value in your mattress purchase.

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gardenguy's Avatar
gardenguy replied the topic: #2 25 May 2018 09:42
Hello all,

I would appreciate someone's input on a DIY mattress I am in the process of making for my office. This will be more of a differential build and is a twin size which I used 6 inches HR foam for the base, 34 ILD-2.6 pound, from foamorder.com. The foam seems to be of excellent quality and has a much different feel than the HD foams I have tested( more rubbery feel and bouncier). It's a very supportive foam for me( 5'10", 145 pound side sleeper), too much so is the issue I have been having, even with top comfort layer . On top of this 6 inches I put 2 inches of 19 ILD blended talalay, the mattress is STILL firm but more tolerable. I am thinking I need either an additional 2 or 3 inch topper on top of this yet, to feel fully comfortable as a side sleeper. I know I don't want this mattress to have memory foam in it. As I see it my acceptable options are another 2-3 inch 19 ILD blended talalay latex, or some kind of HD-HR foam.

This is what I have found so far:
Tuft and needle has a 2.9 pound foam topper with cover in 2 inch for $120 in twin, but they can't disclose the ILD to me, just the pound rating. They can only tell me it feels a medium soft and couldn't tell me if it was HR foam or not, just that it's their proprietary foam. They do have a return policy for 100% refund but it would be a bit of a gamble as far as what it would feel like.

Foamorder.com has a 3.2 pound HR foam called Everflex V24, 24 ILD, and they claim it has durability in the 15 year range. That is 100 dollars in twin. I am not sure if 24 ILD HR foam is an acceptable ILD for a comfort layer, since HR is more supoprtive. I assume it would be less pressure relieving than HD or talalay?

Then there is latex in the 19-24 ILD range, which could work in 2 or 3 inch. I have tried 28 and 14 in the past, for comfort layers, but prefer 19 to 24. I wonder if stacking 3 inches of 19 ILD blended talalay would be too soft over the already existing 2 inch layer. But this is a very firm bed due to the HR foam base being so supportive, maybe I could get away with it.

Those are my 3 options as I see it, but I am just wondering if someone could give me their input on these 3 foams or know of another foam which I don't know about. Would 5 inches of plush over 6 inches firm support be in the realm of normal? I realize I am making up for comfort in the top layers because this HR foam is more firm than I bargained for.
Christeli's Avatar
Christeli replied the topic: #3 25 May 2018 13:07
Have you already adhered the latex permanently to the HR core? If not, a transition layer of about 2" would seem to be what you need. You are on the right track with the ~19 ILD for that. I would look into getting a piece of Energex foam. They make it in 2.5" 20ILD. It is a really good transition layer.
gardenguy's Avatar
gardenguy replied the topic: #4 25 May 2018 13:17
Thank you very much for the reply. Nothing is glued together, just free floating foam layers in a mattress cover. Energex was something I thought sounded intriguing, but I have no idea where to get it. Where could a person get 2.5 inches of 20 ILD?
Christeli's Avatar
Christeli replied the topic: #5 25 May 2018 13:38
I have not looked where to buy it. We use it in our factory. If you search for Energex Topper I would imagine something would come up. If not, let me know and I may be able to help.
gardenguy's Avatar
gardenguy replied the topic: #6 25 May 2018 13:48
I did do a pretty extensive search and all I found was a lot of companies using the Energex name, even some memory foams. To be clear, I do not want memory foam in any way. I would want to order from a reputable company which carries the real energex.