Memory Foam mattresses, like any foam mattresses, are very simple in their construction, yet they can vary from one to another, especially in depth of the mattress and its components and in density these components are made from. There are typically few (2-6) layers of foam stacked or glued together. The bottom layer made from high-density polyurethane (referred to as the Core) is the thickest (4-8 inches) and firmest, providing support for the mattress. Top layers, one or more made from memory foam, are softer providing comfort and pressure relief.
The quality and price of the memory foam mattress depends on the construction of the core and type and density of memory foam used in top layers. High quality mattresses use high-density polyurethane core (6-8 inches) whereas lesser-quality products will either use thinner support layers (3-6”) or lower-density foam. Typical poly core would fall into one of following categories:
Regular Polyfoam (low)- under 1.8 lbs
High Density Polyfoam (medium) – 1.8 to 2.5 lbs
High Resiliency Polyfoam (high) – 2.5 lbs and up
To utilize the entire surface of the mattress and prevent rolling off the bed some manufacturers reinforce the sides of the mattress. Typically they incorporate walls of extra dense foam on both sides or all around the mattress. This design allows for keeping the body in the mattress instead of rolling off. Some manufacturers prefer not to use this type of edge construction because, as they claim, they favor consistent and uniform feel across the mattress.
The upper, comfort layers provide the mattress with softer feel and pressure relief and are typically made from traditional memory foam, gel foam, latex and lower density polyurethane foams. Top memory foam layer is usually 2-6” thick. Thicker layer will allow your body to sink more into the mattress, but using higher density foam can offset it. Higher quality products will typically use 4” or thicker memory foam layer of high-density foam - 5/lbs/ft3 or greater. This way they can provide exceptional combination of support and comfort with high quality foams, offering the best durability but at the much higher expense.