connected by interconnecting wires; encased coils are not connected, but the fabric encasement helps preserve the mattress shape.

There are four types of mattress coils:

* Bonnell coils are the oldest and most common. First adapted from carriage 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,

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