Mattressis a large, rectangular pad for supporting a lying body. It is 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, containing materials such as hair, straw, cotton, foam rubber, or a framework of metal springs. Mattresses may also be filled with air or water.

Mattresses are usually placed on top of a bed base which may be solid, as in the case of a platform bed, or elastic, such as an upholstered wood and wire box spring or a slatted foundation. Popular in Europe, a divan[2] incorporates both mattress and foundation in a single upholstered, footed unit. Divans have at least one innerspring layer as well as cushioning materials.

Mattresses require ventilation to remain dry and prevent mildew, and thus should not be placed directly on the floor or on a solid surface – slats or a box spring provide space for airflow, while solid wood or plywood (as in cheap bunkie boards) does not. Additional ventilation is recommended for natural materials, in which case leaving the mattress "naked" after stripping sheets (for example while laundering) is recommended. If a mattress is allowed to become damp, for example by wet cleaning, mildew may develop inside the upholstery; cleaning with a vacuum cleaner or mild surface cleanser and a slightly damp cloth avoids this.

Excessive wear on mattresses can occur when folding and bending takes place, placing heavy objects in one spot, or excess force on the handles, will also cause more rapid deterioration. Care should particularly be taken during transport or storage.