An Introduction to Differential Construction

Pressure relief and 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.

The advantages and disadvantages to mattresses with differential construction:


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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 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. 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.

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