The United Mattress is a pressure redistribution mattress and not an alternating air pressure mattress. Alternating pressure mattresses have bladders that alternate from inflated to deflated. Every other bladder will be inflated while the other bladder is in a deflated state. The United Mattress works by floating a patient and maintaining low pressure throughout the entire body while not having the constant changes of pressure or alternating each section. Patients find The United Mattress more comfortable since bladders are not changing from inflated to deflated.