Compression Modulus (Support Factor)

[phoenix]

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