Memory foam is made from polyurethane with additional chemicals that add to its viscosity level, thereby increasing its density. It is often referred to as visco-elastic memory foam. Depending on the chemicals used and its overall density, it is firmer in cooler temperatures and softer in warmer. Higher density memory foam reacts to body heat which allows it to mold itself to the shape of a warm body within a few minutes. A lower density memory foam is pressure-sensitive and will mould more quickly to the shape of the body. The example often used to demonstrate its properties is that of a hand pressed into the foam and then removed will leave a clear impression in the foam, then slowly recovers to its original shape.

Memory foam was originally developed by NASA to ease the pressure of extreme G-force during the space programme, and subsequently used in medical applications, for example with patients suffering from pressure sores or bed-bound for a long period.

Memory foam was initially too expensive for general use, 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. 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 pillow may alleviate neck pain. Its heat-retaining properties are also helpful to some pain sufferers, who find the added warmth 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 support of a firm one. Memory foam mattresses often sell for more than traditional mattresses but they can last longer.

When new, memory foam sometimes gives off a slight chemical odor which many people find unpleasant. This will fade after time with airing.

The hardness or softness of memory foam plays an important role in ensuring comfort. Its firmness is determined by its density rating. e.g. 40kgm-3, Soft- Medium  60kgm-3 Medium-High Density. 70-80kgm-3 High Density