Putting the layers together - differential

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:

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”.

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.

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.

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.

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?

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.

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.

Understood. Energex is marketed as having the pressure relieving qualities of memory foam with the durability of Latex. It is really just a high quality polyfoam that is best as a transition layer (in my opinion). If you want me to send you a piece, I would be happy to. Just message me.

I sent you a message. Thanks for the opportunity.

I am not entirely sure this is the correct thread to ask this question, but i will post my query anyway.

I am somewhat a voracious reader of this site over an extended period of time.

I want to know if i am correct in my observation that 2 layers of identical polyfoam combined give better cushioning and support than a single piece(of the same material) whose thickness is equal to the combined thickness of two pieces.

I found mattress made of two pieces of 2.5 lb density polyfoam of 2 inch thickness each has completely different experience compared to a single slab of 4 inch thick foam.

Am i wrong in my observation/reasoning that the first two inch layer behaves somewhat independently from the bottom 2 inch layer ?.
Thanks for giving me the opportunity to post the query.

Hi Rtved.

I am a bit of a bookworm myself and I am glad to have company! …Welcome to our Mattress Forum! :slight_smile:

I can certainly see that you’ve been doing a bit of avid reading on our site as you are asking good questions.

You are correct that the two 2" layer would respond a bit more independently from each other but using two 2" slabs instead a single 4" solid piece of the same foam type (that is exactly the same ILD and density) would make little if any practical difference. In theory the 2 separate sabs would respond independently and they could feel a little softer than a one-piece slab of the same thickness but most people can’t feel any difference at all provided of course that both foams are the same type (density and ILD) and that there aren’t any cutouts or surface modifications such as the layers being convoluted. You can read a little more about some of the considerations of using multiple layering vs one slab in post #2 here.

All the layers of a mattress compress simultaneously, not sequentially, and they will each compress to different percentages of their thickness depending on their position within the mattress, the firmness of each layer, the compression modulus of the material, the thickness of each layer, and the compression force that they are exposed to. Post #4 here has a bit more about the different specs that can affect how soft or firm a foam feels. The two most important of these would be the ILD and the compression modulus although there are also other foam properties that will affect the “feel” of a foam material as well outside of just its softness/firmness that are more subjective.

I hope this gives you a bit more food for thought and satisfies your reading appetite.
Let us know if you have more “queries” and I or any of the Expert members will be glad to assist you.


Thanks for the welcome and the detailed response.I will go through the links.

You are welcome! :slight_smile:


It seems to be very complicate. would you mind that what kind of construction mattress for five stars hotel use ? I am looking to buy for my finished apartment and I am lost how to look for and choose from.

Hi 1liumelion,

There is not a specific answer to this question regarding 5 start hotels, as hotels keep this information private most of the time. Plus our members have mattresses that are much much better than what is found at luxury hotels, many luxury hotels have low-quality mattresses…but have great linens!!!

Check out our members they can help you.


Thanks for your reply. I also noticed that mattress described as similar layers and memory foams, coil spring 12" hybrid and price range from $270 in Amazon to $499, 599 in Costco.Is coils count higher and better? what about weight? Heavier better?
I am shopping for my high end finished apartment, I thought a good quality of mattress is very important. But I just could not evaluate what to buy.
Please help

Hi 1liumeilin,

I totally agree a high-quality mattress is a great idea for a new apartment. Of course, Amazon and Costco may have some high-quality products to choose from.

I highly recommend you take some time to read our mattress shopping tutorial, this article is simply the industries best starting point for buying a new mattress. We spend 1/3 of our lives in our mattress (some more, some less), so we beleive this is a great place to begin getting the information you are looking for.

Thank you,

Hi phoenix :slight_smile:
After long, expensive and fruitless endeavours i stumbled upon mattresses in our relatives home.They were made by a noname fabricator 15 years ago with just a piece of 6" polyfoam.Density is around 2 lb.

I slept on them for a couple of hours and sleep quality is best i had in the last 5 years.to describe i feel nothing while i lie on it.no sinking feeling nor any upward pressure(aka resistance)while i sleep on it.it is a firm foam but one doesn’t feel any resistance while lying on it,which one would experience while sleeping on firm foams.There is no way to know any more details about this foam which i finally found to work for me .it is kind of a unicorn foam.I read somewhere there used to be supplies of no flip polyfoam mattresses of german make about twenty years back.i am hoping(lol) phoenix or other experts/veterans can throw some light on this.

I know of the foam you speak. We have it in a 1994 Winnebago mattress. It is the most comfortable bed foam ever. Not too firm, not too soft, and no odor. Goldilocks (my own name, not a brand name) foam. Have no idea if you can buy it today. Not an expert so can’t throw any light on it.

Hi Rtved,

Good hearing from you again :slight_smile: !

[quote]After long, expensive and fruitless endeavours i stumbled upon mattresses in our relatives home.They were made by a noname fabricator 15 years ago with just a piece of 6" polyfoam.Density is around 2 lb.

I slept on them for a couple of hours and sleep quality is best i had in the last 5 years.to describe i feel nothing while i lie on it.no sinking feeling nor any upward pressure(aka resistance)while i sleep on it.it is a firm foam but one doesn’t feel any resistance while lying on it,which one would experience while sleeping on firm foams.

It looks to me that you are trying to approximate your old mattress from an “unknown fabricator” so I’d keep in mind the following:
• You’d have difficulty matching the all the specs of the particular mattress you describe. Polyfoam relationship of density to ILD is not linear as it is for latex (With latex knowing the density can easily be translated into ILD).
• If you can find the IFD of the poly that the mattress used than you can certainly shop online for a similar mattress. This one would not be too difficult to replicate. Every mattress manufacturer/ retailer has access to and carries 6" polyurethane cores; whether they choose to market them is another question.
• Also, it would be helpful to know what size mattress you are interested and where you are located as perhaps one of our Trusted Members would have answers as well.

And to @Marshmallowforme ….Welcome to the TMU Forum! Thank you for the info you added. However, without a more detailed description and information …It would be quite difficult to ascertain that the bed you mention is the same that Rtved is hoping to find or match. There are hundreds of beds that would match the description: “of 6” polyfoam with Density is around 2 lb."