Memory foam is a type of polyurethane foam that is known for its viscoelastic properties. It is often used in mattresses, pillows, and other products where comfort and support are desired. The density of memory foam can range from 2 to 5 pounds per cubic foot (PCF). The most common density for memory foam mattresses is 4 PCF. This means that amemory foam mattress that is 12 inches thick would weigh approximately 48 pounds.