Memory foam is polyurethane with additional chemicals increasing its viscosity and density. It is often referred to as "viscoelastic" polyurethane foam, or low-resilience polyurethane foam. Higher-density memory foam softens in reaction to body heat, allowing it to mold to a warm body in a few minutes. Faster speed of recovery of a foam to its original shape after a weight is removed is sometimes claimed as an advantage by memory-foam mattress producers, who may talk of "newer generation" foams with "faster recovery.
Memory foam was developed in 1966 under a contract by NASA's Ames Research Center to improve the safety of aircraft cushions. Ames scientist Chiharu Kubokawa and Charles A. Yost of the Stencel Aero Engineering Corporation were major contributors to this project. The temperature-sensitive memory foam was initially referred to as "slow spring back foam"; Yost called it "temper foam". Created by feeding gas into a polymer matrix, the foam has an open-cell solid structure that matches pressure against it, yet slowly springs back to its original shape.
When NASA released memory foam to the public domain in the early 1980s, Fagerdala World Foams was one of the few companies willing to work with the foam, as the manufacturing process remained difficult and unreliable. Their 1991 product, the "Tempur-Pedic Swedish Mattress" eventually led to the mattress and cushion company, Tempur World.
Memory foam was subsequently used in medical settings. For example, it was commonly used in cases where the patient was required to lie immobile in their bed on a firm mattress for an unhealthy period of time. The pressure over some of their body regions decreased or stopped the blood flow to the region causing pressure sores or gangrene. Memory foam mattresses significantly decreased such events. Claims have also been made that memory foam reduces the severity of symptoms (i.e. pain) associated with fibromyalgia.
Source by : https://en.wikipedia.org/wiki/Memory_foam