... spring, spring height 18cm, 1.5cm 30kg/m3 foam around the springi one layer of cotton felt liner ... density. It is often referred to as visco-elastic polyurethane foam. In some formulations, it is firmer when cooler ... . Higher-density memory foam reacts to body heat, allowing it to mold ... in a few minutes. A lower-density memory foam is pressure-sensitive and moulds quickly to the ...