Memory Foam Overview
Memory foam, also known as visco-elastic foam, is a relatively new and increasingly popular development in the foam mattress market. Originally developed by NASA to protect astronauts against extreme “g-forces,” memory foam is known for its ability to mold itself to your body and support it evenly. By making contact with more of your body, the pressure of the mattress is spread over a greater portion of your body’s surface area, thereby reducing stress on your shoulders, hips, and other “pressure points.” It is called memory foam because it is very slow to return to its original shape, thereby “remembering” the shape and contours of your body.
How Memory Foam Works
Made from polyurethane, memory foam consists of billions of little air-filled cells. Like a tiny balloon, each cell contains a small amount of air. However, unlike some other foam cells, memory foam cells actually decompress under pressure, particularly if the pressure is accompanied by heat. Thus, when you lie down on a memory foam mattress, the foam cells closest to your body slowly release their air, creating a unique melting effect and allowing the mattress to conform to the shape of your body. Similarly, when you get up, the foam cells slowly refill with air, which is why it takes a few moments for the mattress to return to its original shape.
Memory Foam Mattress Construction
Memory foam mattresses can differ from one another in a number of ways, most importantly in the density and depth of memory foam used in the mattress’ construction. With memory foam, density can be a determinant of feel, durability, and cost. In general, higher-density memory foams last longer and cost more, and sometimes (but not always) feel firmer. Memory foam density is measured by the weight of one cubic foot of the material — i.e., pounds per cubic foot (lbs/ft3). In mattresses, memory foam can most commonly be found in densities ranging from 2 to 6 lbs/ft3, with most high-quality manufacturers using memory foam with a density of 4 lbs or greater. Most mattresses have a core, or bottom layer, of regular polyurethane foam covered with a top layer of softer memory foam that is anywhere from 2 to 6 inches thick. In general, the thicker the layer of memory foam, the deeper your body will sink into the mattress, which is a matter of some personal preference. Conversely, the denser the memory foam, the less your body will sink into the mattress. Higher-end manufacturers tend to use a thicker top layer (e.g., 3-4 inches or more) of high-density memory foam (e.g., 5 lbs or greater) in such a combination that the greater firmness of the high-density memory foam is offset by the greater depth of the memory foam layer. This approach enables them to create a well-balanced, supportive feel, using foam of the highest durability, albeit at a relatively higher cost.