The major component of memory foam is known as ‘polyurethane’. Polyurethane is abbreviated as PU and is essentially a polymer that is made of organic units. Memory foam is made by adding certain chemicals to the PU, so that its density and viscosity increases. This is also the reason why memory foam is also referred to as ‘viscoelastic’; it’s viscous, yet elastic! That’s why it is categorized as a low-resilience polyurethane foam.