Viscoelastic Memory Foam
Visco elastic memory foam was created by NASA in the early 1970s as an attempt to help the astronauts relate some of the pressures that they felt during take off and reentry. After NASA perfected it with the help of a Swedish foam manufacturer it was soon used in hospitals to help long-term patients. Then in the early nineties a company called Tempur-Pedic created a mattress and began selling it worldwide. Because of the increasing exploding popularity of these mattresses, manufactures from Canada and the United States have begun manufacturing them and selling them to the masses.
One of the problems that people run into when they purchase Visco-elastic foam is that the foam they purchased is not as high quality as it should be. Some manufacturers will charge very high prices from foam that is of much less quality than other versions or other models. This is especially true if you purchase memory foam from your local retail store (stores such as Wal-Mart, target, and Kmart are examples). These companies tend to outsource the manufacture of their memory foam or purchase it from overseas manufacturers. Overseas manufacturers may use toxic chemicals such as formaldehyde and PBDE in the creation of their foam. So not only are these foam products toxic but they also extremely low quality. So to find a higher quality mattress you would need to look for mattresses that are made in the United States or Canada.
So when you're looking for Visco-elastic memory foam, make sure that you check with the manufacturer to find out exactly where the foam was made.