Since memory foam is typically denser than ordinary foam, it is not only more supportive, but heavier as well, providing the simultaneous feeling of support and softness. The density of the foam is temperature dependent and the higher density foams slowly react to body heat slowly, resulting in a soft mold shaped to the warm body, while the lower density memory foams quickly react to pressure more independantly of temperature.
Originally developed by Nasa to help mitigate G-Force pressures, it was never actually used in the space program, instead finding its way into medical products. Memory foam materials are found in mattresses, mattress toppers, and pillows.
Since memory foam is made from organic chemicals, it "out gasses" from the time of production, giving off an identifyable smell. The "out gassing" diminsihes rapidly over time, but some people may occasionally be sensitive to it.
There is actuall a rating for memory foam to reflect its hardness or softness.
The amount of force, in pounds, required to depress a 50 inch disc into a 15"x15"x4" foam sample for two inches is known as one IFD (Indentation Force Deflection) at 50% compression.
An IFD rating of ten would be super soft, while one of 120 would be very rigid.
Memory foam mattresses are typically toward the softer end of this scale.
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