Memory Foam Mattress: Firmness vs. Support

A lot of shoppers confuse support and firmness when looking for a new memory foam or latex mattress that will offer great support. For years, health care professionals have recommended a firm mattress for the best support, but recently the general opinion has shifted. Now doctors say that a softer mattress might indeed offer better support.

So what’s the deal? We can’t have it both ways. I think there is confusion because the advice has not been clearly stated. Experts recommend a bed of a particular firmness for the best support when firmness and support are not directly related. What they should recommend is a bed that:

• Reduces pressure points
• Keeps your spine in a neutral position
• Feels comfortable to you

The firmness of a foam bed is measured in units called ILD’s (Initial Load Deflection). Most latex and memory foam mattresses have top layers from 10 – 20 ILD. Foam ILD is a measure (in pounds) of the resistance foam offers when a large, flat plate is pushed into a block of foam 25% of its total depth. In other words, it measure how firm/soft the surface of a foam block feels. Higher ILD is firmer and lower ILD is softer.

The support of a foam bed is expressed as “support value,” and is derived from 2 numbers: 25ILD and 65ILD. 25ILD measures the resistance of the surface 25% of foam and 65ILD measures the resistance at 65% of the depth of a piece of foam. By dividing 25ILD into 65ILD, you get the support value. Support value tells you how well a piece of foam will support you when you lay down on it. Will it keep your spine in a neutral position, or will it completely compress and let you hips sink too far into the mattress and bump on the harder base layers?