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Compression Modulus (Support Factor) 25 Mar 2015 19:54 #1

Feel free to append this to a related topic if you like. There are a few topics that discuss COMPRESSION MODULUS (aka SUPPORT FACTOR), which you have defined elsewhere as :
(65% ILD divided by 25% ILD) , but this value is seldom provided by retailers (or manufacturers). Do you have any links to (or specs to share) of actual Talalay and Continuous Dunlop Compression Modulus Ratings? You state elsewhere that this is in the 2.5 to 3.0 range for Talalay and more like 4.0 for Dunlop, but it would be good to see some actual mfctr specs, if you can provide them (alternatively, just confirm the ranges for the different types of Dunlop). Also--I found it very difficult to find any HR polyfoam with quoted Compression Modulus ratings over 1.9 . I suspect that Compression Modulus isn't all that significant in a firm HR-PU bottom layer anyway, since it is not deflecting much -- would you agree with that?
thanks

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Compression Modulus (Support Factor) 25 Mar 2015 21:06 #2

Hi Ioway,

I don't have a list of compression modulus specs for specific materials because as you say these aren't specs that are easily available so these are just general ranges. Knowing the compression modulus of a material would also have little practical value when the specs that are already available are already enough to be overwhelming for most people who don't have the knowledge or experience to put them in the context of all the other specs that can make a difference or "translate" them into what they mean in their own personal experience..

Having said that ... there is some information about the support factor of latex in page 3 here (which I believe is talalay latex) and in table 3 here and here (both Talalay) and there is some information about the support factor of Dunlop on page 5 here . There is also a comparison graph that compares the different compression curves of Talalay and Dunlop that gives a good idea of how they compare (see below).

Also--I found it very difficult to find any HR polyfoam with quoted Compression Modulus ratings over 1.9 . I suspect that Compression Modulus isn't all that significant in a firm HR-PU bottom layer anyway, since it is not deflecting much -- would you agree with that?


You're right that information about compression modulus/support factor is also difficult to find for specific types of polyfoam although you will find this more easily than you will for latex. As you also mentioned though ... it's a more important factor in upper layers that are compressed more deeply than it is in deeper layers which don't deflect as much so the 25% IFD would be more important for the deeper layers.

Phoenix
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Last edit: by Phoenix.

Compression Modulus (Support Factor) 26 Mar 2015 09:33 #3

Loway, just in case you want a bit more information about compression modulus / support factor for polyurethane foam, PFA has some information here :

I am in total agreement with Phoenix that, 1: CM/SF information is difficult to come by, and 2: for most people it tends to muddy the waters rather than clarify.
Jeff Scheuer, The Beducator™ Owner of Mattress To Go
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Compression Modulus (Support Factor) 26 Mar 2015 21:11 #4

Phoenix:
Thanks--some good references. A couple of those references got pretty deep into the weeds, but I at least skimmed them all. I also saw where a third term "Sag Factor" is also used interchangeably with Support Factor and Compression Modulus (you'd think the industry would stick with one term). The last link you gave from Latex Int'l with the hysteresis graphs tell the story pretty well in comparing Dunlop compression to Talalay. This matches what I feel in the samples-- at 50% compression, Talalay's increase in ILD remains fairly linear (through about 75% compression), whereas at 50% compression, Dunlop becomes very firm/non-linear. This may be a useless discussion for most folks, but it helps me to understand the application and effects of the different types of foams better in upper/lower layers and for pressure relief vs support. I think one of the most ambiguous terms in this discussion of compression modulus is the term "support." Whereas Dunlop will rapidly increase in firmness after 50% compression (what is called "support"), that same property can create pressure points to hips and shoulders that sink into this deeper/firmer zone, but since Dunlop is relatively soft (relative to the 25% ILD rating, that is) in the upper 25% of the layer, it can actually have diminished support to other parts off the body that need more support. The properties of Talalay are clearly better than Dunlop in this regard in the top layer as you can have the same ILD, but have more support in the top 25% and less pressure points in that 50-75% depth. I suspect some HR polyfoams would have similar characteristics to Talalay (especially in 2" layers). I am concluding that (for me) Dunlop is a good middle layer, but is not ideal for the top (unless you need firm), which is what is stated elsewhere in different ways, but at least I now have a good understanding of how the properties of the foam types are accomplishing this.

Thanks for all the good advice on this Forum and for hosting this site!

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Last edit: by Ioway. Reason: not done

Compression Modulus (Support Factor) 26 Mar 2015 21:26 #5

MattressToGo: thanks. Another good reference

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Last edit: by Ioway. Reason: not relevant, reduce forum noise

Compression Modulus (Support Factor) 26 Mar 2015 22:34 #6

Hi Ioway,

I also saw where a third term "Sag Factor" is also used interchangeably with Support Factor and Compression Modulus (you'd think the industry would stick with one term).


There are a few other terms that are also used as well including SAC factor, comfort factor, hardness ratio, and modulus ( see here ) just to confuse things even more (although you rarely see SAC factor or hardness ratio used)

This may be a useless discussion for most folks, but it helps me to understand the application and effects of the different types of foams better in upper/lower layers and for pressure relief vs support. I think one of the most ambiguous terms in this discussion of compression modulus is the term "support." Whereas Dunlop will rapidly increase in firmness after 50% compression (what is called "support"), that same property can create pressure points to hips and shoulders that sink into this deeper/firmer zone, but since Dunlop is relatively soft (relative to the 25% ILD rating, that is) in the upper 25% of the layer, it can actually have diminished support to other parts off the body that need more support.


I differentiate "support" into two different types that I call primary support and secondary support depending on whether you are talking about upper layers or deeper layers. You may have read this already but there is more about primary or "deep" support and secondary or "surface" support and their relationship to firmness and pressure relief and the "roles" of different layers in a mattress in post #2 here and in post #4 here that may be helpful in clarifying the differences between firmness and "support" and "pressure relief" and "feel".

I suspect some HR polyfoams would have similar characteristics to Talalay (especially in 2" layers).


HR polyfoam by definition has a density of 2.5 lb/ft3 or higher, a compression modulus of 2.4 or higher, and resiliency of 60% (measured by ball rebound) so it can approach the specs of Talalay and some of the newer higher density/high performance polyfoams (that range from about 2.5 lbs to 5 lb density) can be manufactured to approximate the specs of latex as well.

Phoenix
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Last edit: by Phoenix.
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