Metal-Fabric Springs.
The least expensive, and the least serviceable, are the fabric springs. They consist of a flat layer of crossed or meshed wires which are fastened to the frame with helical springs. As they are subjected to continuous downward pressure they will soon develop a sag. These should be used only with solid-filled mattresses. Another type of fabric springs consists of steel bands fastened to the ends of the frame by helical springs and to each other by short helical cross ties or wire locks. The higher priced models of this type provide a good foundation for an inner-spring mattress.
Figure 27.—(Upper view) Platform-top coil spring.
Figure 27a.—(Lower view) Open-coil spring to be used with solid mattress.
Open-Coil Springs.
The open-coil springs are built to provide flexibility and are particularly designed for use with solid-filled mattresses. They consist of spiral coils, larger and stronger than those used in inner-spring mattresses, set into a metal frame. Each coil usually is held to its neighbor by four small helical springs. The coils are supported at the bottom by metal strips running from one side of the frame to the other.