A box spring is a type of bed base designed to support a mattress. It typically consists of a wooden frame covered in fabric, with springs or a solid platform inside. The primary purpose of a box spring is to absorb shock, provide stability, and extend the life of the mattress. Box springs are often used with innerspring mattresses, but they can also be paired with other types, such as foam or hybrid mattresses. They come in various sizes to match standard mattress dimensions, including twin, full, queen, and king.