Memory foam is typically made of polyurethane. Memory foam mattresses are well ventilated to prevent the buildup of heat, sweat, and dust mites in the mattress. Memory foam has a high resilience which provides shooting comfort by absorbing pressure points on your body when you're lying down. They also have denser internal structure that typically makes them heavier than spring mattresses. The density also means they don't sink in much over time, making them easier to lift for regular cleaning or flipping the mattress over every few years.