Memory Foam - Properties

Properties

A memory foam mattress is usually denser than other foam mattresses, making it both more supportive, and heavier. Memory foam mattresses are often sold for higher prices than traditional mattresses.

The property of firmness (hard to soft) of memory foam is used in determining comfort. Firmness is measured by a foam's indentation force deflection (IFD) rating. However, it is not a complete measurement of a "soft" or "firm" feel. A foam of higher IFD foam but lower density can feel soft when compressed.

IFD measures the force (in pounds-force) required to make a dent 1 inch into a foam sample 15" x 15" x 4" by an 8-inch-diameter (50 sq in) disc—known as IFD @ 25% compression. IFD ratings for memory foams range between super soft (IFD 10) and semi-rigid (IFD 120). Most memory foam mattresses are firm (IFD 12 to IFD 16).

Some report that IFD is a poor way to measure softness of memory foam, and that foam density as a measure of quality is more important, but not always true. Foam density of 5 pounds per cubic foot (80 kg/m3) or greater is considered high quality, although most standard memory foam has a density of 1 to 5 lb/ft3 (16–80 kg/m3). Most bedding, such as topper pads and comfort layers in mattresses is 3 to 4.5 lb/ft3. Very high densities such as 5.3 lb/ft3 (85 kg/m3) are used infrequently in mattresses.

Memory foam has an open-cell structure that reacts to body heat and weight by 'moulding' to the sleeper's body, helping relieve pressure points, preventing pressure sores, etc. Most memory foam has the same basic chemical composition, however the density and layer thickness of the foam makes different mattresses feel very different. A high-density mattress will have better compression ratings over the life of the bedding. A lower-density one will have slightly shorter life due to the compression that takes place after repeated use.

Cell structures vary from very open, to almost closed cell. The tighter the cell structure, the less airflow through the foam. "Breathable" visco-elastic foam will have a more open cell structure, allowing higher airflow, better recovery, and lower odor retention at packaging. The cell structure has little to do with the slower or faster recovery.

The amount of memory foam also has an effect on the capabilities of the mattress or topper. Anything less than 2 inches will not have much of an effect, whereas a 6-inch block would be too soft and dense to sleep on comfortably.

The properties of a mattress depend upon its height, density, and type.