Coil System

Spring mattress core

The core of the mattress supports the sleeper’s body. Modern spring mattress cores, often called "innersprings," are made up of steel coil spring, 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; pocketed coils are not connected, but the pockets preserve the mattress shape.

There are four different types of mattress coils most commonly used:

• Bonnell coils are the oldest and most common. First adapted from bugguy seat springs of the 19th century, they are still prevalent in less expensive mattresses. Bonnell coils are hourglass-shaped, and the ends of the wire are knotted or wrapped around the top and bottom circular portion of the coil and self-tied.

• Marshall coils, also called "pocketed coils," are each wrapped in a fabric encasement and usually are tempered, or in the case of the Simmons Beautyrest carbon magnesium is added. Some manufacturers pre-compress these coils, which makes the mattress firmer and allows for motion separation between the sides of the bed.

• Offset coils (LFK) are designed to hinge, thus conforming to body shape. They are very sturdy, stable innersprings that provide great support.

   

• Continuous coils Or Mira-coils, Work by a hinging effect, similar to that of offset coils. In a basic sense a continuous coil is simply that, one continuous coil in and up and down fashion forming one row (usually from head to toe) of what appear to be individual coils. The advantages of how firm a support the continuous coil provides it is somewhat tempered with the 'noise' associated from a typical mira coil unit.