Foam Mattresses & Support Factor

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Foam mattress support goes hand in hand with pressure relief as the two most important qualities of foam mattresses. Foam support factor is how foam engineers quantify and talk about how well foam gives support. It is calculated based on two measurements of firmness:
 
1)   25 IFD – The number of pounds it takes to compress a piece of foam 25% of its height.
2)   65 IFD - The number of pounds it takes to compress a piece of foam 65% of its height
 
The formula for support factor is:
 

What Does Support Factor Tell Us?

Support factor tells us that different foam mattresses respond to pressure in different ways.
 
1)   Foam mattresses can be soft on top and firm as you push deeper into the mattress, providing good support.
2)   Foam mattresses can also be soft on top and soft as you push deeper into the foam, providing little support.
 
Some foam beds increases resistance very slowly as you apply pressure. Other foam beds increase resistance very quickly as you apply pressure. Support varies widely among foams from different manufacturers.

Foam Mattresses Use Layers to Provide Proper Support

Foam mattresses are built up from 2 or more layers of different kinds of foam, firmer base foam layers on bottom and softer memory foam layers on top.
 
The cumulative effect of the layers should be to absorb the pressure applied by your body, one layer pushing down into the next. Heavier parts of your body, like your hips and shoulders, push down more deeply into the layers, while lighter parts find all the support they need at the top of the bed.
 
Layers that work well together create a foam back support mattress. The proper support relieves pressure and eases back pain, allowing deep sleep.

How Can Foam Support Factor Help You Select a Memory Foam Mattress?

Will it help you to know the support factor # of a mattress when you are comparison shopping? No, it won’t. Even if it did, support factor is not made available outside the plant where it’s poured. But there is a good reason to have an understanding of how engineers think about support.
 
If the top memory foam layers provide too little support, and the base layer is too firm, you can “bottom out.” This causes pressure points.
 
Good foam mattresses absorb pressure and provide support without bottoming out. If the mattress is comprised of layers of varying firmness, the mattress can potentially provide better support and pressure point relief; but they must work well together.