The Bonnell is the classic spring unit, and had through the years, proven its worth. This spring is hour glass shaped with knotted end rings at top and bottom front sides. A round helical wire connects each single spring along a line either head to toe or side to side. A border wire support goes around the perimeter clipped to each spring on the outer edge of the unit.

When little weight is applied, the mattress with the tailed springs is softer because the resistance is still low. Then, when more weight is applied, the resistance to the body weight is higher and is increased with the degree of the compression. The number of springs is one of the key quality characteristics. Bonnell spring units are a reasonably priced high quality spring system used in medium quality mattresses, provide excellent support and comfort.