A few DIY questions.

So I’ve been visiting places in the Seattle area, and I’m just not finding what I want at a reasonable price. I’m pretty convinced that the DIY is the way to go for me, but I’m trying to get as much info as a I can about it before I do it.

First of all, and this is a doozy, but does anyone know of any online resource that gets into the real technical aspects of how latex foam distributes weight, preferably in relation to its ILD rating? I have spent a good two or three hours looking for this information, and it’s nowhere to be found. If not that, could anyone help me understand how weight distributes through latex in a more general sense? I would imagine that low ILD foam would mostly distribute weight straight down, where the higher ILD’s would distribute it both down and to the sides.

The way Custom Sleep Design uses lower ILD for your shoulder is genius. My current memory foam mattress raises my upper spine about 2 1/2 inches above my lower spine (we put tape on my back and took pictures, no wonder this mattress is killing me). In an effort to sink my shoulder further than my hips I would love to try something similar. Does anyone have any experience with this? I would assume I would need to glue to the two pieces of foam together. Is that pretty much beyond the DIY ability? If not, what kind of glue would you use? I couldn’t really find much info on this.

Here’s what I got when I plugged all my numbers into CSD. I took the liberty of putting the ILD numbers in there.

And Here’s what I’m thinking I will attempt to build. I’m going to use a solid layer for the top to try and avoid the issue of seams.

The average ILD of the top 5" for the head side came to an average of 20 ILD
The average ILD of the top 5" for the foot side came to an average of 30.4 ILD

With my setup, I would be looking at an average of 22 ILD for the head and 26 ILD for the foot. I’m going to work those numbers a bit more. I might do a 4" core, and I might bump the foot side up to a 36 ILD. but overall this is what I am planning to do for now. Any thoughts or recommendations would be appreciated.

Hi BloodSyphon,

Latex re-distributes weight and reduces pressure in the same was as any other foam except different types of latex have different specs which would affect weight distribution differently (just like other foams have different weight distribution profiles).

Some of the information that you may find helpful (some of which are fairly technical which you wanted :)) includes this article, along with post #2 here and post #26 here and post #2 here and post #4 here, and post #6 here, and post #4 here.


I definitely get the impression you feel foam math is a pipe dream, which I can’t disagree with. It’s just kind of shocking how little information is actually available. In my mind, there has to be exponential formulas for how different ILD’s compress. Obviously if I had the test equipment and a bunch of foam I could figure it out, but I figured at some point someone had to have done this testing. It looks like you actually did this a bit with some dunlop, but then you just did some linear math. You mention that it’s actually a curve, but you didn’t get into that. I’m going to have to let this one go.

On the cutting and gluing of foam, do you have any experience with that Phoenix? Do you have any recommendations on how to make clean cuts in foam and how to create seams? I use a hot wire cutter to chop up insulation foam to make airplanes, but I’ve read both good and bad things about trying this with latex foam. The general impression I get is that it doesn’t work, and I imagine it would leave a hard edge where it cut.

Hi BloodSyphon,

I think that the idea of producing a meaningful formula to build a mattress based on foam compression or hysteresis curves would be a pipe dream yes. The foam information exists and there are quite a few diagrams of the hysteresis curves of different types of foam you can find with some digging but this type of information still wouldn’t be particularly meaningful without a 3 dimensional model of the person and the constantly changing surface areas of the body that are compressing the foam as they change position. It would also need to take into account the different stresses inside the body rather than just the skin to surface pressure mapping. I’m currently reading this book for example which has more advanced math in it than i could possibly understand but takes into account both the materials and the characteristics of the human body and how it interacts internally and externally on support systems.

Very little first hand experience (with some cutting only not gluing) but lots of second had talking with people who have done so and an electric knife works very well if you go slowly. Local fabric or foam shops will sell you spray glue that works very well for gluing foam together.


“I’m currently reading this book for example…”

Just reading the table of contents was too intense for me and I’ve designed a university’s remote robotic observatory. Did you make it through that beast and what was the most important thing you learned from that comprehensive rabbit-hole-of-a-book?


What is your take on the Custom Sleep Design?

Do you think there would be a problem with the seam in terms of feel?

Hi Prof_Admiral_H_Nelson,

No not yet … I haven’t even had close to the time to do much reading with the things that need doing on the site in the short term even though I’ve ordered another book as well that I’m looking forward to that isn’t quite as intense (and I may end up reading first as a warmup to the other one).

A lot of the math is beyond me but I’ve been reading parts of it as I have the chance. My other half has a bachelors in nuclear physics from many years ago so she may have to translate some of the math for me or at least give me a primer. While its too early to say anything for sure … I think the thing that has stood out so far is how differently internal body tissues react to pressure than most people who studied these things seemed to previously believe. They built a model that is a very close approximation of the human body for their research. It shows that the pressure on the skin surface may have little bearing on what is happening inside the body in the deeper tissues (bones, joints, ligaments, muscles, etc). It’s complex enough that it will be slow going to get through it.

Like all the members here I think very highly of them and I like how they zone and customize their mattresses. You can read more of my thoughts about them in post #8 here and post #4 here.



Greetings BloodSyphon,

 I've cut 3 inch layers with no problem using an electric carving knife.  If you cut along the pincore holes its very easy to keep your cut straight. Plus there is a lot less material to go through.  Takes less than a minute.  I haven't tried gluing them back together yet.  Still "researching".

I can’t comment on your chosen ILD’s because everyone is different. I think your idea of a single top layer is good. I cut my top layer and it shifts a little now and then.

Unless you’re very tall, I think your 36" cut is rather long. Since your not cutting your top layer, the cut in your second layer could be closer to your waist.

If you go soft in the shoulders, it might feel heavenly on your side, but could roll your shoulders forward (scrunch?) on your back.

The cover you use makes a real difference in how much your shoulders plunge.

Good Luck, brotherloo

I have been sleeping on my CSD mattress for a little over a week. You cannot feel the seem between left and right, or even within a layer, at all through the cover. Let the pro do the cutting and measurements if you can. Those pieces of foam are very unwieldy, and CSD encases each layer (cut into several different pieces) in one thin cover. I highly recommend my CSD mattress (split firmness/sides – one at 125lbs and 185 lbs) and have recommended friends too at this point.

the reason I decided against zoning for my DIY mattress is because I like to sleep in different positions. if I always slept on the back zoning would be something to look into however foam is usually sold in standard bed sizes so it would cost more to go with zoning.

Thanks to all!