NASA developed what has become to be called the memory foam mattress in the 1970's. Since then the visco elastic foam, sometimes referred to as NASA foam mattress, was first used in medical settings to prevent pressure sores. The mattress was used on beds and for padding for wheelchairs.

NASA foam mattresses are measured by the indentation load deflection measure (ILD). Basically, the ILD is a measure of the firmness of the mattress. In other words, it is a standard measure of how deep you will sink into the mattress if you sit on it.

An ILD between 10 and 11 is considered soft. An ILD between 12 and 16 is considered firm, and an ILD between 16 and 20 is considered extra firm.

We've all seen the commercials for memory foam showing how it forms to your body and gives support. But for the average consumer, there are more things to consider. What are the different types, what are the advantages and disadvantages, and of course, how much is it going to cost?

ILD is not the only thing to consider. The density of the foam is important also. Foam density is measured in pounds per cubic foot. Mattress with less than 3 pounds density will not provide enough support. Dense foam is more durable and better for support. Dense foam will also more heat.

Visco memory foam mattresses range in price from around $300 to well over $1000. The price difference is mostly dependent on the size of the mattress. The quality of the foam also effects the price. Memory foam mattresses are typically more expensive than spring mattress counterparts.

Memory foam is different from regular foam. When you lay on visco elastic foam, the heat from your body causes it to flow. The foam will contour to your body. When you get up, there will be an indentation in the shape of your body. After a while, when left undisturbed, the foam will return to its original state.

The major advantage of memory foam mattresses is the your weight is evenly distributed by the foam. There are no pressure points such as may occur with a spring mattress. This is why NASA foam mattresses were tried in medical setting for bed ridden patients.

Another point for memory foam, is that motion is not easily transferred. That means if you share a bed with a partner, your partner's movements will not transfer to you resulting in a more restful nights sleep.

The biggest disadvantage of this style of mattress is that is traps much more heat than a regular mattress. While this may be an advantage in the winter, it is a disadvantage in the summer.

New mattresses often have a chemical smell and may require airing out prior to use. Also, be aware of lower priced mattresses. These are often inferior products.