A box spring is a type of bed base typically consisting of a sturdy wooden frame beneath a steel inflexible grid, covered in cloth. Usually, the box spring is placed on top of a wooden or metal bed frame which sits on the floor and acts as a brace. The box spring is usually the same size as the mattress above it. Working together, the frame, box spring, and mattress make up a bed.
The purpose of the box spring is threefold:
- to raise the mattress height, making it easier to get in/out of bed;
- to create flat firm structure which reduces wear on the mattress;
- to conserve the fashionable look of the bed.
With the increased height of mattresses today, manufacturers now make box springs in different heights. Standard box springs are 9 inches in height, whereas "low profile" box springs are 5 inches. The difference between the two heights is purely aesthetic and makes no difference in the support provided for the mattress.