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Questions about Compression Modulus
One possible explanation is that you use Talalay and they use Dunlop? In that case why would ild be rated the same while actual firmness is so different?
Here is the article, by the way: www.kttenterprises.com/technical-blog.html
The indenter used in ILD testing has the surface area of 50 square inches. And it needs the force of 200,000 Newton to compress 4'' talalay in the above graph to 40%. That means that 200 lb person would need to apply all his/her weight over the surface area of 2.36 square feet to really notice the difference between Talalay vs Dunlop. Average body surface area of 200 lb person is about 21 square feet. So one needs to apply all the weight on about 11% of your body. Even sleeping on the side, this is impossible.
Talalay sellers always say that it is softer than Dunlop, while Dunlop sellers say this is not true: sleeponlatex.com/blogs/news/7845413-dunl...s-talalay-latex-foam . According to physics, Dunlop sellers are correct. There might be a difference in feel, but not firmness. In fact, according to the above graphs (which comes from Talalay seller KTT Enterprises) dunlop will be about the same or slightly softer for most people.
I was scanning through your multiple postings across many forum topics and had to quickly step in as some of your postings can more confuse than help clarify questions of topic initiating poster.
You have brought up several issues in different topics not the least of which is the danger of reading too much into online reviews of any type (see post #13 here)
Let me dispel the myth that Talalay is Softer than Dunlop.
While education and research is key in finding a good product that matches all your personal criteria I’d caution against making such general blanket statements as there is really no "standard" type of feel or “standard” perception of softness /firmness of Dunlop vs Talalay latex. Aside from any scientific data or experiments, generally applying such "standards" can be not only confusing to the average consumer but challenging even to those with many years of experience in mattress design mainly because it all plays out in a larger context of how all layers work together and also personal needs and preferences for an individual sleeper. There are too many interacting variables of different ILD's, different layer thicknesses combinations and firmness levels, latex types, and different ticking/quilting combinations that can have a big effect on the mattress and can have a very wide range of different feels and interact very differently with different people (BMI, where the weight is carried, sleeping stile, body surface in contact with the mattress.. etc). This is one of the main reasons we’ve started the “Ask an Expert” program on our forum. The many years of experience with materials, and product designs but most of all … how different body types and individual sleeping styles respond to the multiple variables involved in mattress construction is why I so often recommend to rely on the advice of a manufacturer (that has your best interests at heart) as they are much more familiar with their own mattress/topper designs and materials than anyone else (including me or other forum moderators) and they can use the information provided about body type, sleeping positions, preferences, history on different mattresses, and the results of any local testing to make suggestions based on the "averages" of other similar customers.
There is a technical spec for foam which is called compression modulus which is the ratio between the force needed to compress a foam to 25% and the force needed to compress the same layer to 65% of it's thickness. 65% is exactly 2.6 times 25% which means that a completely linear compression rate would have a compression modulus of 2.6. This is approximately the compression modulus of Talalay latex.
For the hybrid versions, you mention... it generally known by experts that springs have a similar measurement called spring rate. Because they are linear ... a single spring which has the shape of a cylinder and has even turns will have an equivalent spring rate of 2.6 (because it would be compressing 2.6 times as far). This means that the compression modulus of Talalay and the spring rate of a cylindrical spring would be similar. Dunlop has a higher compression modulus so it would get firmer faster than this same type of spring ... but this is where the similarities end. Most springs have a softer section and a firmer section (which can be achieved with different shapes such as thinner and thicker diameters in parts of the spring or different gauge springs on top of each other and in other ways as well). This means that this type of spring would have multiple spring rates. You can see some graphs of the response of variable rate springs here and you can also see a typical compression curve of Talalay latex here directly from TG’s older article about it.
If you would like to dive a little deeper into technicalities, it would be best to move this discussion to a different more relevant topic so as to keep the original Poster’s more focused on the topic he started in AP’s forum. (You can do a quick Forum Search to look for a thread that closely matches your subject of interest.)
Thank you very much for your comment, I really appreciated it. I agree with everything you said in the first long paragraph. The "feel" can be very different, as well as interaction between layers, and even covers can combine to result in a very different cumulative outcome.
May I just make one comment here as part of this thread discussion? I understand compression modulus, but my point was that in any sleeping position it is almost impossible to compress latex beyond 40% by an individual under 200 lb, so comperssion modulus is not very relevant in real life situations. Below 40% compression, both Dunlop and Talalay have very similar curve (second image in the article you linked to). So, I just don't understand when experts on this forum say without reservation that Talalay is softer; I hope someone will explain what they mean because it is not in agreement with the article be in terms of force and pressure (as well as Sleep on latex website). My other main point in previous comments was that often repeated statement on this site that heavier people should sleep on firmer latex goes very much against my personal experience (I am out of $450 because of such comments ).
For the last 1.5 months, we were sleeping on a 3'' latex topper at 30ild (on foam). I found it way too firm (200lb) while my wife found it soft (130lb). It agrees with latex response curve. It feels soft at low compression and quickly firms up as with compression. So for a heavier person like me it becomes like a rock. I actually folded it in half and slept on a 6'' layer of 30ild. It was better but still had an uncomfortable shoulder pressure with a cover on top. This observation seems to agree with Spindle mattress configurations . They call 20ild latex "medium" and 30ild latex "firm", and their soft, medium, and firm configurations all have 20ild layer on top. Only extra-firm has 30ild on top. And this is for 9'' mattress which should feel softer than 6''. At 6'' at 20ild would be firmer than what they call "medium". This agrees with my experience, so I don't understand why some people on this site keep saying that adults need to sleep on firmer latex?
For clarity and for other consumers who may be following the responses unrelated to OPs original question, I am renaming this portion of the thread to "Questions about Compression Modulus" and moving the posts to the General forum space. Hope this helps…