Memory foam is made from polyurethane with additional ingredients that add to its
viscosity level, thereby increasing the density of the foam. It is often referred to as visco-
elastic polyurethane foam. Depending on the chemicals used and the overall density of
the foam, it can be firmer in cooler temperatures and softer in warmer environments.
Higher density memory foam will react with body heat and allow it to mold itself to the
shape of a warm body within a few minutes. However, a lower density memory foam
is pressure-sensitive and will mold more quickly to the shape of the body. The example
often used for a demonstration of its properties, is a hand pressed into the foam and
then removed, leaving a clear impression of the hand in the foam.
Memory foam was originally developed by NASA to ease the pressure of extreme G-
force during space shuttle take off. While memory foam was never used in the space
program, it was subsequently used in medical applications, for example when a patient
suffered from pressure sores or had to be bed-bound for a long period.
Memory foam was initially too expensive to own by the general public, but in recent
years it has become cheaper to produce and is now widely available. Its most common
domestic applications are mattresses, pillows and mattress toppers (also known as
mattress pads). It remains useful in medical-related uses, such as wheelchair seat
cushions, hospital bed pillows, and padding for persons suffering long-term pain or
postural problems; for example, a memory foam cervical pillow may alleviate chronic
neck pain. Its heat-retaining properties are also helpful to some pain sufferers, who find
the added warmth also helps alleviate pain.
A memory foam mattress is usually denser than an ordinary foam mattress. This makes
it more supportive – but also heavier. It is often seen as a good compromise between
the comfort of a soft mattress and the supportiveness of a firm one. Memory foam
mattresses often sell for more than traditional mattresses but last longer.
When new, memory foam often gives off a distinct chemical odor which many people
find unpleasant. This fades with airing; however, some people remain sensitive to it.
The hardness or softness of memory foam plays an important role in ensuring comfort.
Memory foam firmness is determined by its IFD rating. Indentation Force Deflection
measures the amount of force, in pounds, required to indent a 50″ inch disc into a
15″x15″x4″ viscoelastic foam sample and make a 1″ indentation. This is commonly
known as IFD @ 25% compression. Unlike other types of polyurethane foam, memory
foam has the ability to change firmness with temperature (it becomes firmer when
colder and softer when warmer).