Components of an innerspring mattress

The core of the mattress supports the sleeper’s body. Modern spring mattress cores, often called "innersprings," are made up of steel coil springs, or "coils."

The gauge of the coils is another factor which determines firmness and support. Coils are measured in quarter increments. The lower the number, the thicker the spring. In general, higher-quality mattress coils have a 14-gauge (1.63 mm) diameter. Coils of 14 to 15.5-gauge (1.63 to 1.37 mm) give more easily under pressure, while a 12.5-gauge (1.94 mm) coil, the thickest typically available, feels quite firm.

Connections between the coils help the mattress retain its shape. Most coils are connected by interconnecting wires; encased coils are not connected, but the fabric encasement helps preserve the mattress shape.

Here are four types of mattress coils:

• Bonnell coils are the oldest and most common. First adapted from buggy seat springs of the 19th century, they are still prevalent in mid-priced mattresses. Bonnell springs are a knotted, round-top, hourglass-shaped steel wire coil. When laced together with cross wire helicals, these coils form the simplest innerspring unit, also referred to as a Bonnell unit.
• Marshall coils, also known in the industry as wrapped or encased or pocketed coils, are thin-gauge, barrel-shaped, knotless coils individually encased in fabric pockets—normally a fabric from man-made, nonwoven fiber. In the case of Beautyrest, high carbon magnesium is added, while the steel itself remains untempered. Some manufacturers precompress these coils, which makes the mattress firmer and allows for motion separation between the sides of the bed.
  

  

  Bonell springs
• Offset coils are an hourglass type coil on which portions of the top and bottom convolutions have been flattened. In assembling the innerspring unit, these flat segments of wire are hinged together with helical wires. The hinging effect of the unit is designed to conform to body shape. LFK coils are an unknotted offset coil with a cylindrical or columnar shape.
• Continuous coils (the Leggett & Platt brand name is Mira-coil) is an innerspring configuration in which the rows of coils are formed from a single piece of wire. They work in a hinging effect similar to that of offset coils.

The bed coil spring was patented by Louis Andrew Vargha.

[edit]Air mattresses

Air mattresses use one or more air chambers instead of springs to provide support. Quality and price can range from inexpensive ones used occasionally for camping, all the way up to high-end luxury beds. Air mattresses designed for typical bedroom use cost about the same as inner-spring mattresses with comparable features.

[edit]Air mattresses as regular beds

Several companies currently produce adjustable firmness air mattresses. In 1981, Comfortaire began manufacturing and marketing an air bed that looked like a conventional inner spring bed, but allowed users to adjust the firmness. Select Comfort patented a variant and began marketing them in 1987. Today, Select Comfort produces the "Sleep Number" bed which, in some models and sizes, allows independent adjustment of each side of the bed for comfort and firmness.