I am looking at adding a 1" transition layer between a 3" latex topper and 8" of coils to act as sort of a buffer layer as the 3" latex topper is on the soft side of things (19ILD). I think I remember reading on here that ILD’s of polyfoam are measured differently then latex. I had been looking at 1" of medium firmness dunlop around 28-30ILD but then found I can get 1" of polyfoam for a third the price also at 28ILD. While I know the feel would be different I am wondering how much I need to take into account for firmness differences between the two or does it not matter as much since I am only using 1"? Would 1" be enough to act as a transition layer or should I look at potentially a different set up?
Hi landale1,
There isn’t an exact answer to your question, as there is much more to take into account than simply the difference in ILD of the materials (density of the polyfoam would be one). But I think you’re referencing a previous post where I spoke about how ILD in latex is usually measured with a 6" thick layer of foam and it’s basically the weight that it takes to compress a 50 sq in round metal foot into the foam by 25% (which would be 1.5"). This is different from polyfoam which is measured with a layer of foam that is only 4" thick so it would only be compressed by 1" (and the ILD number would be lower than latex). So first of all latex ILD is not directly comparable to polyfoam ILD. Some latex manufacturers also produce cores that are a different thickness which would also produce a different ILD rating compared to testing ILD on a 6" core. There are also different latex testing protocols for ILD so in some cases the ILD would be tested at 40% compression instead of 25% compression which would also produce a different result.
Different materials including latex have a variance across the surface of the 6" core so in one place it may be say 24 ILD and in another part of the core it may be 22 or 26. the ILD rating is usually an average of the range across the surface. Blended Talalay has less variance (=/-2 or so) than Dunlop which may vary by more (+/-4 or so). 100% natural Talalay can have a larger variance than blended Talalay.
Polyfoam also would generally have a lower compression modulus than either Dunlop or Talalay latex, although HR polyfoam has a compression modulus that approaches Talalay latex. Granted, you’re only considering a 1" piece of polyfoam in this case.
Overall, the uppermost layer of your mattress (the 3" of latex) will most dramatically impact your comfort, and if you’re going to select a polyfoam 1" layer to place beneath it, I would choose a higher density piece (2.5 lb with at least a 2.4 compression modulus will have resilient properties similar to latex) and something in the ILD range you mentioned is considered common for average seat cushions, and a 30-36 ILD range is common for firmer seat cushions and mattresses, with 36-45 ILD common for firm mattresses (see section 4.2.2 here). So something in the upper 20 to mid-30 ILD range would be common for this application, and is commonly used as a transition layer in traditional innerspring mattresses.
Phoenix
Thanks! It looks like good quality polyfoam that is more than 1.8lbs would cost me close to $60 for an inch. I can get a medium density dunlop latex layer for just over $100 so I might as well just spend the extra money and avoid polyfoam entirely.
Hi landale1,
You’d probably be happy with either, but with the relatively small increase in price to choose latex, it certainly makes it worthy of consideration.
Phoenix
Sorry, one last question. As I mentioned the top layer is a 3" 19ILD talalay topper which is quite soft, probably a touch softer then I would like. Will going firmer on the transition layer help in a sense firm up the comfort layer since layers will sort of act together? My other thought is that since the cover I bought is pretty stretchy I can probably fit another half inch of dense polyfoam into the cover under the coils, which I imagine in turn will firm up everything?
Hi landale1,
You are correct, all of the layers of a mattress work together in unison, and placing a firmer transition layer beneath your upper comfort layer and on top of your springs will change how you “bend into” the mattress and will create a bit of a more firm comfort. Placing a small amount of foam on the bottom of the mattress under the springs will not have as dramatic an impact on your surface comfort, and you might not even notice .5" of foam placed upon the bottom of the springs.
Phoenix
Thanks, that’s what I figured on the middle layer so I am looking at a 1" layer of either D75 or D80 dunlop latex to go between the coils and soft top layer.
In regards to the half inch of polyfoam under the coils I didn’t think it would change the feel just by itself but that it would stretch out my cover which is designed for only 12" but could almost certainly stretch to 12.5" and then put more compression on the top layer, thus making it feel a bit firmer.
Hi landale1,
You are exactly correct with that statement about the cover. I was going to add a comment to that effect yesterday, but most people don’t take the time to get that deep into the detail of construction and at times I tend to get too esoteric with my explanations, but it is good to see you are considering such things! The impact of this of course would depend upon the style of cover you have (less dramatic with a stretch-knit versus a thicker cotton/wool quilted over that is stiffer), and of course would be minimized over time as the cover breaks-in and loses some of its “false firmness”.
Good thinking! B)
Phoenix
[quote=“Phoenix” post=72439]Hi landale1,
You are exactly correct with that statement about the cover. I was going to add a comment to that effect yesterday, but most people don’t take the time to get that deep into the detail of construction and at times I tend to get too esoteric with my explanations, but it is good to see you are considering such things! The impact of this of course would depend upon the style of cover you have (less dramatic with a stretch-knit versus a thicker cotton/wool quilted over that is stiffer), and of course would be minimized over time as the cover breaks-in and loses some of its “false firmness”.
Good thinking! B)
Phoenix[/quote]
I only thought about it as my previous mattress was significantly firmer then expected due to a very tight cover design that I failed to take into account for (from the side measurements it looked like the 3" of dunlop latex were compressed down to close to 2"). My cover is a stretch-knit so I don’t expect a significant change but I am only looking for a slight firming up of the support as I love the plush top but at the same time I wouldn’t mind minimizing overall sinkage in my heavier areas by 1/4 to 1/2".
I also imagine adding a half inch of dense 2.5lbs 50ILD polyfoam under the coils would make the mattress a bit more forgiving of my slat set up that I have right now as a foundation.
Hi landale1,
All excellent points, and using the very firm polyfoam layer under your pocketed spring unit will tend to work better with a slatted network. Good thinking!
Phoenix