A foundation designed to support an innerspring mattress. Better mattresses use heavy coils. Mattress coils are absorbed by the box spring, prolonging the life of your mattress. A box spring and mattress together are referred to as a set.
Also referred to as a "foundation". A base for a mattress, consisting of coils or other forms of springs or steel grid-work mounted on a wood or metal frame and secured with a wire-interlaced or welded-wire grid, topped with upholstery and insulating materials (felt, urethane or other resilient materials), and covered on the top and sides with ticking and on the bottom with a dust cover.
It features extra-heavy-duty springs. If the springs match the mattress it is called a coil upon coil box spring. Since a box spring has coils, it generally increases the give in the mattress, which in turn produces a softer or bouncier feel.