US Patent 8714531 Telescoping spring assembly for mattresses and the like

A spring assembly includes telescopically adjustable inner and outer members biased in an extension direction by a coil spring. A non-stretch fabric sleeve fitted about an inner diameter and an outer diameter of the coil spring is closed at its opposite ends to apply a compression preload to the coil spring. The fabric sleeve prevents transmission of the preload to the inner and outer telescoping members, thereby eliminating stickiness and the popping sound that are drawbacks of the prior art, and the fabric sleeve also provides general noise reduction when the spring assembly changes length.