Latex Firmness Measurement

Discussions General Mattresses Questions
1

First of all, I appreciate Phoenix for this forum and the knowledge he imparts on us everyday. Thanks Phoenix.

Few weeks ago, I started doing research to buy a new mattress to replace the Memory Foam mattress. Went to few brick and mortar stores to try the beds. One thing I was certain was that memory foam mattress is not for me. This feeling was enforced by the trials in the stores. All the beds I tried are inner spring mattresses and I can rate them subjective on the scale of good to bad, but nothing really stood out.

After few hours of googling, I decided to try out latex mattress before selecting an inner spring mattress. After trying out the latex mattresses in a store (not going to mention any names at this stage), I am convinced latex is the answer to my search. Both the latex mattresses I tried had three 3" layers of latex. Mattress 1 had Dunlap firm bottom, dunlap medium middle and Talalay soft top, and Mattress 2 had Dunlap firm botto, Talalay medium middle and Talalay soft top. Liked both mattresses. Thought Talalay medium and Talalay soft mattress would be ideal for a side sleeper for me.

Retail price of these mattress in the store are little over my budget, so purchased a king bed with both the configurations. My initial impressions are , bed is not as soft/comfy as the one I tried in the store and Dunlap firm, dunlap medium and talalay soft side feels slightly softer than dunlap firm, talalay medium and talalay soft side.

To bring objectivity to my subjective impressions, I need to measure the firmness (ILD) of each layer on both sites. While it is impossible to accurately measure the ILD at home on a 3" slab, a DIY contraption can be made to measure the relative differences in firmness between the layers. Atleast in my case, since all the slabs are of same thickness, the measured relative differences in firmness should be valid.

My idea of a cheap DIY contraption is to use a circular base of about 8" diameter and stack weights on it.

This website, pfa.org/jifsg/jifsgs4.html , says about 28lbs/50" sq pressure is needed to deflect 25" in a 4" slab. Going by that estimate, I assume I would need weights in the increments of about 1/2 lbs from 18lbs to 35 lbs.
ADMIN NOTE:Removed 404 page link | Archived Footprint: pfa.org/jifsg/jifsgs4.html

I can use circle made of MDF (medium density fiberboard) as the base.
Any ideas what materials are readily available in the market to use was weights? My initial idea was to use clutch plates, but they might not be heavy enough to make it practical. Weights need to be about 1/2 lb and stackable.

2

DUH moment. Barbell weights.

3

Hi Keyser,

Welcome to the Mattress Forum! :slight_smile:

You’re welcome.

I’m a little confused here :S . Do you mean that you tested a latex configurable mattress in a brick and mortar store, but then purchased latex components online to create your own DIY latex mattress?

I’m not sure what you’re attempting to accomplish here, as your own subjective testing of how the mattress feels will be the most reliable indicator of your preference of comfort. If you’re simply testing to see how much weight can compress into each piece of foam and know that a “firmer” piece will require more weight to compress than a “softer piece”, my guess is that you already know this as the different pieces of latex you ordered would have been identified as such and most likely given an ILD range.

ADMIN NOTE:Removed 404 page link | Archived Footprint: pfa.org/jifsg/jifsgs4.html

Those are specifications for polyfoam IFD measurements, and they are not relatable to ILD numbers of latex, as latex tests (usually) a 6" piece versus 4" for poly foam. The ILD of different materials or even different types and blends of latex also aren’t always directly comparable to each other (see post #6 here). Measuring the same tyoe of foam (latex) but changing the thickness of the foam sample tested also changes the results and the numbers would not be relatable due to the differences in the rate that a foam “firms up” as it is compressed.

ILD can be measured in different ways (different piece thicknesses, different dimensions of the tested piece, different disc sizes, different percentages of compression…). And ILD isn’t the only factor that affects the softness or firmness of a material so again using the ILD or other specifications of a particular layer or combination of layers as a reliable indication of how any mattress will “feel” or how firm it will feel to you compared to another mattress with a different combination of layers can sometimes be more misleading than helpful, and wouldn’t replace your own personal testing.

While your experiment might be a fun process to go through, you won’t arrive at any meaningful information that would translate to any ILDs offered to you from a manufacturer of foam pieces you may be considering either online or from a brick and mortar retailer, as your testing methods will be quite different from what the industry uses, as explained in the earlier post I linked to.

Phoenix

4

After reading reviews of latex mattresses, I wanted to try it out to determine if I would like Latex. Found a store in my area which carries latex mattresses, do tried them and liked the feel of latex mattresses than any inner spring mattresses I tried.

To save $$$ I purchased a split-king mattress with three layers of 3" latex foam. Its not DIY.

Absolutely agree. I am not subjectively satisfied with this mattress at this time. Its on the hard side and springy feeling. Maybe sleeping on it for a couple of weeks might change my opinion, we will see.

My biggest surprise is, dunlap firm, talalay medium, talalay soft does not feel softer than dunlap firm, dunlap medium, talalay soft combination. In the store, I could feel considerable difference between the two combinations.

Is my memory playing tricks on me? Possible. Shall go back to the store and try again. But, I also want to confirm the three layers are really hard, medium and soft. One of the layers has manufacturer label (see pic). Looks like the density is between 85-90 and HD (ILD?) of 40.33.

I read the ILD of the firm should be about 29-31, medium 24-26 and soft between 19-31. If my firm layer has ILD of 40.33, its is extra firm. The firmness difference between Dunlap firm and dunlap medium is very little.

I am trying to establish a firmness relationship between the three layers, not measure actual ILDs. That might also answer why I do not feel Talalay medium/Talalay soft combination is softer than Dunlap medium/Talalay soft combination.

You are right, ultimately my subjective experience is the only thing that matters.

5

Hi Keyser,

Thanks for the clarification. It seems you tried some latex mattresses but then purchased a different one from another store (that was more affordable), this with different configurations on each side.

All latex will tend to have a buoyant and “springy” feel (it is foamed rubber), but some of that can wane over time. The product, especially the covering, will “break-in” a little after the first month or so and will become a bit softer and it loses some of its “false firmness”.

Dunlop tends to feel a bit softer when initially compressed as compared to Talalay, but then firms up faster (higher compression modulus). The layers closest to your skin will have the greatest impact upon comfort, so with the change in the middle transition layer between the two models you are trying, the difference would be down to the “medium” layer of either Talalay and Dunlop, and while both are labelled as “Medium” could be quite different in actual ILDs. Depending upon the time the floor model was on display in the showroom you tested can also impact the difference in comfort. Also, there may have been a change in suppliers for the foams used by the store between what the floor model used and what you received (you’d have to check with the store fi that happened). And above all, ILDs are “ranges”, so there will be variability.

I don’t know that the 40.33 (or 40-33) is an ILD measurement of that piece of foam, as Latex Green use kgf (kilograms of force) for their pieces. The more important number would be the density.

Here are some “approximate” ILD numbers for Dunlop latex (there is quite a bit of variability here):

EXTRA SOFT 16-18 … 4.05pcf (64.9 kg/m3)
SOFT 19-22 … 4.36pcf (69.8 kg/m3)
MEDIUM 23-27 … 4.67pcf (74.8 kg/m3)
MEDIUM FIRM 28-33 … 4.98pcf (79.8 kg/m3)
FIRM 34-38 … 5.30pcf (84.9 kg/m3)
EXTRA FIRM 39-44 … 5.61pcf (89.9 kg/M3)
X-EXTRA FIRM 45-49 … 5.92pcf (94.8 kg/m3)

The closest way to make meaningful comparisons between different Dunlop cores would be through density comparisons. These will not always be identical between different manufacturers and layers though because with Dunlop there will be a variance in ILD/IFD in different areas of the layer surface and there will also be a variance that depends on whether a layer was cut from the top or bottom of a 6" core (the whole core is assigned the density rating but the top 3" would be less dense than the rating (softer) and the bottom 3" would be denser than the rating (firmer) even though both cores would generally be “rated” to match the whole core). There would also be some slight differences in different latex foam formulations, different latex hybrid species or production years of latex raw materials, and variations in the method of manufacturing the core. In spite of all of this … density comparisons or ILD/IFD comparisons (if they are correctly assigned) or better yet both would be the most accurate way to make the most accurate possible comparisons. If for example one layer has a density of 85 kg/M3 and another is 75 kg/m3 and the higher density latex is being rated as the same ILD/IFD or “word rating” as the lower density version then I would be asking some questions about why and probably assume that one of them has been incorrectly rated or with different criteria. The better manufacturers will use ILD/IFD or word ratings that are fairly consistent across their different materials and they will be very informative in a conversation about how their different options compare so you can get a good sense of how they may feel but this may not always “translate” well between different manufacturers.

This gets confusing though because different materials and different areas of the world use different methods of measurement. Some latex (like talalay which is produced in 6" cores) for example measures ILD @ 25% with a 6" slab (which would then be rated higher than a 4" piece) while some areas of the world use ILD @ 40% compression instead of 25% which also results in a firmer rating. Other areas or materials ( such as latex green) use kgf (kilograms of force) which “looks like” much softer latex than a standard ILD test would produce (notice how low the numbers are). Sites all over the internet have simply posted the kgf rating except they call it ILD which is quite misleading as to how soft/firm it really is so some people that are using Latex Green layers for example believe that they will be softer than they really are and may have great difficulty getting their layering right. Because of the variations … it is sometimes difficult to “translate” the softness or ILD of materials from one measurement to another unless the differences are taken into account or known through experience.

Double checking everything with your retailer would indeed be the best place to start.

Phoenix

6

Phoenix,

Thanks for the reply. This is an educational experience.

Called the vendor, he suggested I try to bed for a few more days before deciding to return. Agreed to try until next weekend.

While I agree in general, it is not a rule. Most of the material would fall within a range of density would have ILDs with in the a predictable range, but not always. According to the Latex Green website, the bottom layer of my mattress under two different comfort categories, Medium-Firm for density and Extra-Extra-Firm for hardness

http://www.latexgreen.com/cores.html

While discussing the density and hardness numbers on the Latex Green label, vendor asked if the density is between 85-90 (which it was) and claimed they only go by density numbers in choosing the layers. That may be the problem why this mattress is so firm. If one is going by only 10 point range of hardness to categorize the cores as soft, medium or hard, their ILD rantings could fall well outside the ILD ranges for the same category, as my bed.

Between density and hardness, I think hardness is more important as it contributes more to comfort factor.

7

Hi Keyser,

I would agree with the vendor as well, as you haven’t had the mattress very long. Many stores and online vendors would ask that you keep a product for at least 30 days to get a true sense of your affinity for the product and allow the mattress to adjust to you and you to adjust to the mattress.

Density is the more appropriate manner for comparing and rating Dunlop latex, for the reasons I described and linked to earlier and the inconsistencies in establishing ILDs with Dunlop. It is the reason why many Dunlop latex producers even refuse to use ILDs in describing their products.

They don’t list ILDs. They list a range of Kgf. They are not the same.

This would be correct and accurate.

This is a firmer piece of Dunlop latex, that is true. As if the feel is too firm for your preference, you certainly may with to go with a lower density.

Some Dunlop latex companies offer latex in 5 Kg/M3 steps, but there will always be overlaps as it is not exact. A 10 Kg/M3 +/-5 spread is common. The tolerances for Dunlop latex are generally not as tight as for Talalay latex.

The density is how the “hardness” is most appropriately expressed and related in Dunlop latex, and there is a direct relationship between the two. A denser Dunlop latex will be harder than one that is less dense. When comparing latex from the same supplier using the same fillers (or lack thereof), the same vulcanization process, the same mixture and type of latex, the same height of the cores and the same size and distribution of the pin-holes, the density will be number that relates comparative firmness. It’s what the Dunlop industry uses as guidance and is most accurate. While you personally may feel that an ILD is more important, it would be a less accurate manner of comparing Dunlop latex (and of course the many different manners of assessing ILD) and it’s an opinion that would not be shared by Dunlop latex foam fabricators or designers.

I would avoid getting too caught up in technical specifications and simply realize that if you desire a softer product, you’ll go with a less dense piece of Dunlop latex.

Phoenix

8

Actually, both ILD and Kgf are measuring the same property of the mattress, hardness. Only difference is the units of measurement. Its like measuring my weight in pounds or kilograms. Just as the ILD numbers increase, the mattresses gets harder, increasing Kgf numbers would lead to increasing hardness of the mattress.

My only point is, Latex Green is classifying kgf numbers in the range of 27-33 as “extra-firm”. The bottom layer of my mattress has Kgf number of 40.33 which means it is lot harder than extra-firm. My order was for a “firm” in the bottom later.

And ofcourse, you are right, density of a mattress does have a direct correlation with hardness, but that correlation is not constant. For the correlation to be constant, there cannot be any other variables between the pours. If there is a variation in either the chemical composition or vulcanization processes, the density/hardness ratios would wary. That does not mean the latex cores with higher hardness for a given range of density are faulty, far from it. They are just harder cores, that all.

Only the densities cannot be used to gauge the hardness of latex. That is the reason manufacturers publishes both density and hardness numbers.

Anyways, I will sleep on it for another week and reevaluate.

Added:
Also, all the retailers I have seen classify the mattress in terms of hardness, either ILD numbers or name classifications like extra-soft, soft, medium, firm or extra-firm etc. Virtually no one classifies the mattresses on the basis of weight (density) like light, medium and heavy, extra-heavy etc. We feel the hardness of the mattress, not its weight.

9

Hi Keyser,

Yes, I mentioned this in one of my earlier posts. ILD can be measured in pounds and kg. Also in kPa (kilo Pascals) or Newtons.

As I mentioned previously, I didn’t think that the 40.33 (or 40-33) listed on your tag was a Kgf number (or any other sort of ILD number), and I’ve confirmed with a supplier that it is some sort of an internal tracking number. It could be a batch number, a run number, or some other internal quality control number. Maybe even the mold number. So hopefully that doesn’t concern you as much moving forward.

Yes. This is all information explained in more detail in my previous posts and items linked within those posts.

That is incorrect. As I explained and linked to in my earlier replies, because of the variation in the Dunlop production process, the difference in where the foam was sliced from the production core, and the various differences in testing used for Dunlop (ISO 2439 - 25%, 40%, 60% - and ISO 3386, for example), and how Dunlop “firms up faster” after 25% deflection, many Dunlop manufactures will not provide ILDs in any form, only densities and “word ratings”. The density is the most consistent and accurate way to rate and compare Dunlop foam, and is what the industry uses. While ILDs and densities are not “exact” numbers, but instead fall within “buckets”, a core rated at 85 Kg/M3 will always be harder feeling than a core at 75 Kg/M3. If you had your own mattress manufacturing company, you would be ordering your Dunlop via density, not ILD. Granted, the “word ratings” can be confusing, as what one latex pourer may call “medium” might be called “medium-firm” by another brand (depending upon the differences in the number of densities they pour and their manner of differentiation), and might also be called something else by a mattress manufacturer. But the density number will be consistent and more reliable for comparison between any product using Dunlop latex, for the reasons of differences in measuring ILD I mentioned earlier.

Yes, ILDs for Talalay (and sometimes Dunlop) are used by some mattress manufacturers as descriptors of the foam layers, although most common would be “name” classifications, as that would be most relatable to the general public. When looking at individual Dunlop layers, again “name” classifications would be most popular, but density is quite often used, and sometimes even ILD (or all three, such as here). Using the density of mass per unit volume to describe the Dunlop does give a consumer an idea of hardness, but as you mentioned no one takes mass and (as is done often in common usage) and refers to the weight of a layer of foam, as in the mattress industry this has no basis for reference like density does and would not make sense to the general public, and is something I’ve not mentioned or ever seen done.

Phoenix

10

Good point. I cannot be absolutely sure that the number listed as “HD 40.33” is the hardness measured in Kgf. But, that I find unusual is the supplier cannot tell what that number represents but rules out that it it represents hardness. Unusual indeed. I would say, none of us know what “HD 40.33” represents with any degree of certainty.

Latex Green’s messaging system on their website is not working. Shall try to call them next week to seek their input.

Me and my daughter went to HealthyBack stores this evening to try out their latex offerings. Both of us felt the softer side of my mattress is a lot firmer than Healthy Back’s medium bed, Essence.