A mattress is a large, rectangular pad for supporting the reclining body, designed to be used as a bed or on a bed frame, as part of a bed.Mattresses may consist of a quilted or similarly fastened case, usually of heavy cloth, that contains materials such as hair, straw, cotton, foam rubber, or a framework of metal springs. Mattresses may also be filled with air or water. Tips and comparisons to help you choose the best mattress. Every person has unique set of considerations when it comes to finding the best mattress, including sleep position, health concerns, firmness preferences, and personal size and shape. .