First, not all memory foam mattresses are alike. There are many different styles associated with viscofoam mattresses with many different features.
However, in general, most memory foam sleep systems consist of a visco elastic or memory foam layer of body weight and body temperature sensitive pressure relieving viscoelastic material for comfort.
This memory foam material consists of thousands of tiny cells which constantly readjust to any pressure placed on the memory foam. This memory foam material is in fact five times denser that regular foam used in other traditional products.
The support core in a memory foam mattress layer usually consists of either 100% natural latex, Talalay latex or blended latex in most high-quality memory foam mattresses, or polyurethane.
The core layer in memory foam mattresses provides the much needed pressure point relief, which causes discomfort, as well as back support.
Optional 'Tri-Layer' design
Recently, a third layer has also been introduced to the memory foam mattress market called the Tri-Pedic™. This memory foam mattress was introduced by Dr. Rick Swartzburg, D.C. based on the theory that while 5lb density memoryfoam mattresses will provide much more support and temperature sensitivity, they were usually a bit more costly than 4lb density memory foam mattresses.
The Tri-Pedic™ is basically a more cost-effective memory foam mattress, with a hypoallergenic & ventilated velour stretch cover, consisting of two 2-inch layers: a 4lb density viscoelastic foam layered on top of a 5lb density memory foam layer. Beneath these two layers is a supporting high resiliency polyurethane base.
Some additional options:
In addition to the basic counterparts of memory foam mattresses, many brands add other materials for extra comfort such as high quality wool layers, convoluted memoryfoam layers (allowing for more airflow through memory foam layers), and lyocell (made from wood pulp) covers.