Memory foamwas launched in 1966 to improve the aircraft cushion's safety. Technology released the new type of foam to the public domain in the 80s.  Memory foam was consequently utilized in medical set ups.  It was usually used in cases when it was necessary for patients to stay on bed immobile for long hours.  Memory foams decrease the risk of pressure sores that firm mattresses result to.  This new developed foam was too expensive but as time went on, it has become less costly.  Its most forms are mattresses, pillow and mattress toppers.  Until today, memory foam mattresses are still used medically for its advantages in alleviating chronic pain.

Characteristics and Advantages
Memory Foam is polyurethane with chemicals increasing its density and viscosity. It is sometimes known as visco-elastic polyurethane foam.  Higher density memory foam responds to body heat, making it mold a warm body quite some time. Lower density memory foam is sensitive to pressure and forms immediately to the shape of the body.
For an object to be visco elastic, it must be sensitive to temperature and has the capacity to rebound quickly and go back to its normal shape.  Memory foam is categorized by its durability and visco elasticity by the following grading scheme.

1. Indentation Load Deflection
The rating will tell you the hardness or the softness of the material.  The higher the     Indentation Load Deflection (ILD) the firmer the foam.  Mattresses with lower ILD are an advantage in pressure point decline.  But despite the material's softness without good support under can also be problematic to some users.  Memory Foam Mattresses have both the lower ILD and the support through layered materials to offer a flexible surface to distribute pressure points.

2. Weight
Amount of chemicals in the composition of the polyurethane foam determines the foam's weight. Visco-elasticity and density are higher if more chemicals are used. Memory foam mattresses use 3lb to 5lb chemicals to maintain its advantage.

3. Tensile
This is the extent to which the foam can be stretched, elongation of stretch before rupture, measured in pound per square inch. Memory foam mattresses cannot be easily damaged because they don't stress but are only compressed once lied on.

4. Resilience
This determines the rebound percent of a ball dropped from a 36 inch height.  In traditional foams, the higher the rebound the higher is the durability. However in memory foam mattresses, the less resilience the better is the dampening force. High quality memory foam mattresses mix lower resilient layers with memory foam on the surface so you get the decrease of pressure points while maintaining the support underneath.