Memory foam mattresses can come in many different firmness levels. When you are shopping for a memory foam mattress, it is important to know what type of feel you like. Memory foam can be very soft and marshmallow-like or very firm, just sinking in slightly when you lie on it. There are multiple factors that determine how firm or soft a memory foam mattress will feel and not all of those factors are determined by the memory foam itself. All memory foam mattresses are made in layers. Memory foam is the top layer(s) and base foam are the bottom layer(s) that form the foundation of the mattress. No memory foam mattress is made of just memory foam. There is always some type of base foam beneath the memory foam.