Today, most mattresses are manufactured according to standard sizes. This standardization was initiated by the industry to resolve any dimensional discrepancies that might occur between companies that manufacture beds and companies that make mattresses. The sizes include the twin bed, 39 inches wide and 74 inches long; the double bed, 54 inches wide and 74 inches long; the queen bed, 60 inches wide and 80 inches long; and the king bed, 78 inches wide and 80 inches long.
The “core” of a typical mattress is the innerspring unit, a series of wire coils that are attached to one another with additional wire. The upholstery layers are affixed to the innerspring: the first, called the insulator, is fitted directly onto the innerspring and prevents the next layer, the cushioning, from molding to the coils. While the insulator is fairly standard, the number of cushioning layers can vary widely in number, ranging from two to eight layers and from 1/4 inch to 2 inches (.63 to 5 centimeters) in thickness. Moving outward, the next component is the flanges, connecting panels that are attached to the mattress’s quilted cover with large, round staples called hogs rings. The top, bottom, and side panels of the mattress are stitched together with border tape.
While a wide variety of springs are designed to accommodate special needs and situations, the four most commonly used coils are the Bonnell, the Offset, the Continuous, and the Pocket System. The Bonnell springs are hourglass-shaped and knotted at both ends. The Offset design is similarly hourglass-shaped, but its top and bottom are flattened to facilitate a hinging action between the coils. The Continuous innerspring consists of one extremely long strand of steel wire configured into S-shaped units. Finally, in the Pocket System, each coil is encased in a fabric casing that also connects it to neighboring coil-casing units.
A typical mattress contains between 250 and 1,000 coil springs, and mattresses that use fewer coils normally require a heavier gauge of wire. It is not uncommon for an innerspring unit to require as much as 2,000 linear feet (610 meters) of steel wire. The individual coils can be joined in several ways. One common method is to use helicals—corkscrew-shaped wires that run along the top and bottom of the springs, lacing the coils together. Rigid border wires are sometimes attached around the perimeters to stabilize the unit.
Most manufacturers also produce foundation mattresses or boxsprings that lie directly beneath the mattress, resting on the frame of the bed. One of the most common types of box spring foundations uses a spiked coil configuration, in which the springs are narrow at the bottom but spiral to a wider diameter at the top. While a spring system provides the most common type of boxspring support, torsion bars are also sometimes used. Other foundation mattresses contain no springs at all but consist of a built-up wooden frame.