Memory foam consists of low-resistance, or viscoelastic polyurethane, and several other chemicals, such as hydrocarbons. Medicine ball sinking into Nectar Premiere’s memory foam Compared to polyurethane foam, this material is denser and more temperature-sensitive. Generally, it becomes softer and sinks more in response to body heat. What is memory foam made of? Memory foam, also called viscoelastic polyurethane foam, combines some chemicals compounds and additives to polyurethane polymer. When added to the polymer, the compounds increase their elasticity and density, and that factor allows the foam to contour to your body. i8kwkH.