Includes all the mattress support layers below the quilting and comfort layers.
Also called visco-elastic or slow response foam, it is a special formulation of polyfoam which changes phase and becomes partly viscous instead of elastic with the application of heat and pressure. This allows it to form a very conforming pressure relieving cradle. It also has low resilience and when softened with heat, humidity, or time typically has a very low ILD (usually below 18).
Are “mini” inner springs designed specifically for use as part of a comfort layer of a mattress and can be both pressure relieving and supportive.