Hi RSZ,
Another bed that we liked was the Tempur-Pedic Contour Signature. We went twice this weekend to try this bed out. Layed on it for a good 15 to 20 minutes. What we found was it was very conforming and gave you that sleeping in sand feeling, which we actually like. The only problem was my wifes hip started to develop a pressure point, and felt hard on her hip. For me, it was my shoulder that felt like it wanted another inch or two to sink into to.
this is fairly "typical" of the difference between male and female physiology. Women tend to have wider hips and they are a common pressure point while men tend to have wider shoulders and narrower hips and experience more pressure issues there. In both cases ... it points to a thicker/softer comfort layer being necessary than the Contour signature provides (although like most memory foam mattress it would soften during the initial break in period as well).
After trying out a bunch of beds the past week, I'm more curious to find out more the WHY of how and why that Bellafina bed feels the best.
I have my suspicions, that given our "stats" that 3" or 4" in the comfort layer is not giving us enough room to reduce the pressure points in the hip area for my wife, and the shoulder area for me. So the Bellafina with 3" in the top memory foam coupled with the 3" of latex is giving us 6" of comfort layer. While that middle three inches of latex is probably, as you suggested, probably somewhere in between a comfort layer and a support layer.
The why and how may be more complex than you imagine and is difficult to "nail down" without knowing the specifics of the materials (which you won't be able to find out to the level that may be necessary) but in essence the reason is a combination of the balance between the "comfort zone" of each mattress which provides the cradle and pressure relief and the support layers which "stop" the heavier parts of the body before they sink in too far. The middle "transition" layer (like the latex in the BellaFina) can play a role in both because the top part of the layer would be softer but latex has a higher compression modulus than polyfoam and gets firmer much faster with deeper compression so it becomes a support layer once it compresses to a certain degree. In other words ... ow much of the latex adds to comfort and how much of it adds to support varies with different body shapes and weights. It's more adaptable than other materials.
I would personally trust your own personal testing rather than going down the road to "designing" your own mattress to the last detail based on specs which can be as misleading and confusing as they can be helpful. Enough information to make good choices and working with an "expert" can be very helpful but too much information and analysis which replaces your personal experience in local testing can often lead to paralysis by analysis and overthinking the construction of a mattress.
We went into Custom Foam on Friday, they have their Simply Perfect mattress set up to try on the floor with 3" 5lb gel infused memory foam over 5" of 2535 poly. My first impression, is that I would like at least another inch or two of foam on top, it felt HARD. Hard in the sense that within 5 minutes I felt I wanted my shoulder to sink in more. My wife's initial impression was she wanted her hips to sink in more, and have more pressure relief in the hip area. It felt like we bottomed out of the memory foam. So my first reaction with that mattress would be to add another inch or two of memory foam, and make the base 6" of 2535 or 2545 poly. We both feel that 3" of MF doesn't provide enough of a cradle.
I would trust your impressions here about the thickness of the memory foam given your other feedback and considering that the Contour Signature with 4" of memory foam was also a little too firm (although each different type of memory foam ... even of the same density ... can respond differently to heat, weight, and pressure.
They also have a all poly mattress set up that is all 2527 poly. It also felt too thin, but it felt much like latex.
yes ... 2.5 lb polyfoam ... if its HR grade ... has many (but not all by any means) of the qualities of latex. HR polyfoam is really the closest you will come to the feel and performance of latex in polyfoam.
I would also be aware though that ILD (IFD in polyfoam) may not translate directly from one material to another because they are tested in different ways
I understand that there is no way to tell 100% how all the layers would interact with each other and the final feel of the bed. Thinner layers gives the option to swap out layers without incurring crazy costs.
This is very true ... but only to a degree. layer thickness plays an important role in the feel and performance of a mattress and if there are too many thin layers it will change the feel compared to thicker layers and it can become very difficult to know what to change and the thickness of each layer can become an additional variable where the effect on the mattress may have to "intuited" rather than analyzed. This is why personal testing and reference points can be so important because the body feels all the layers as a whole rather than each layer individually.
Custom Foam have 2527,2535,2545 poly as wall as 4lb MF, 5lb MF, 6lb MF, and the 5lb gel infused MF. The gel infused MF felt slightly firmer than the regular 5lb MF.
They certainly have the raw materials that would give you all the choices you need. The extra firmness of the gel memory foam is typical because the gel tend to increase the compression modulus of memory foam which is as much a part of how firm a foam feels as ILD or layer thickness (and temperature response in the case of memory foam as well).
It seems to me that you have some very good material options for a "design your own' mattress but as you know the challenge will be trying to predict how these specific materials will interact together with each other and with you and because of all the variables involved this is as much based on intuition as it is on specific technical analysis.
What I do know for certain is that I will be crazy by the end of this process!
As long as it's "good" crazy

then by the end of it you will know more about mattress theory and design than most people and you will have the satisfaction of sleeping on your own custom design. It's a fascinating and never ending learning curve. If frustration or confusion (vs interesting questions) starts to creep in though then is the time to pull the trigger on what you believe is best for you and let the experience of your body tell you how you did and what may need to change. I can't even begin to tell you how many times I have spend hours in a "relaxed" mode trying to visualize how a certain combination of materials would interact and the 'reasons" behind it.
I will be very interested in watching (or commenting) your journey and seeing what you come up with.
Thanks for all your feedback so far ... and I get the impression as well that custom foam/the foam store in Kitchener are good people to work with.
Phoenix