Numerous options exist for classifying support surface technologies. Here, technologies are classified according to their mechanical characteristics or unique therapeutic function. In practice, most products consist of a combination of materials and incorporate multiple therapeutic strategies. Available seating products generally fall into the categories of compressive support mediums (elastic foam and viscoelastic foam), fluid-filled, and alternating pressure. Available bed support surfaces also fall into the same categories with the addition of air-fluidized and low air loss. In this section, we describe the characteristics of products falling into the various categories and discuss their performance relative to their pressure distribution, shear, temperature and moisture control. Examples of representative products falling into these are given in Table 1. This list is included to illustrate the types of products included in the categories and is not intended to be comprehensive.