Spring Mattress Core

The core of the mattress is the most important part in the support of the body. In most modern mattresses (except for foam-only ones), it is made up of steel coiled springs, also known simply as coils. The spring mattress core is also called innerspring. This provides support to the set. Proper support is where the wire coils push back in response to weight deflection to hold the body in alignment. The steel coil spring was invented during the industrial revolution and was first patented for use in a chair seat in 1857. Then, in 1871, Heinrich Westphal invented the innerspring mattress. He lived in Germany and died in poverty, having never profited from his invention…

When does a mattress need replacing?
After 7–15 years, depending on use and quality, although many people use their mattresses longer.
Experts indicate that two adults sleeping nightly on a queen mattress will notice the padding, not the coils, breaking down after a period of four to six years. While the mattress will still be comfortable, it will no longer feel the way it did when first purchased.
When laying a hand on the mattress with about three pounds-force and sliding it over the mattress lumps can be felt.
When the user regularly wakes up feeling tired, stiff, achy and sore and the reason can be traced to the mattress.
When inner coils start springing out of the mattress.
When the mattress shows very visible deformities.
When the mattress has a large permanent sag in it.
When the box spring creaks and squeaks.
When the user has difficulty finding a comfortable position in which to sleep.

Types of coils

Construction-wise, most manufacturers claim to have the best coil-to-gauge ratio. However, there are only a few innerspring manufacturers and four general types. One thing to remember is that while there are many different types of coils and many manufacturers, most manufacturers have their coils made by one company, Leggett & Platt, at least in the Western Hemisphere

Bonnel coils

These are the oldest and most commonly used. They were adapted from buggy seat springs of the 19th century. They are still prevalent in low priced mattresses. They have an hour-glass shape, and the ends of the wire are knotted or wrapped around the top and bottom circular portion of the coil (round-topped and self tied).

Marshal coils

Also called “pocketed coils.” Each coil is wrapped in a fabric encasement, and is usually tempered twice, once with heat and once with electricity. The brand Simmons uses pocketed coils in their mattresses. Simmons also does some things that other brands that use pocketed coils don’t. They “pre-compress” their pocketed coil, which means that they pack the coil into a “pocket” that is shorter (usually by a couple inches) than the coil. By “pre-compressing” the coil, it becomes firmer (sort of) because the coil is already in action (it is always pushing up.) Additionally, when two people sleep on the same mattress, the individually wrapped (or individually pocketed) coil provides motion separation (when one person tosses and turns, the other doesn’t feel it.) This is important because when one person tosses and turns, it may not completely wake the other person, but, it can take them out of a deep sleep which is when the body does all of its regeneration.

Offset coils

Bonnell coils evolved into Offset coils, which are currently popular, but happen to be the most expensive ones. They are almost identical to the Bonnell coils, except that the top and bottom circular part of the coils have flat or straight sides, which allow for better hinging action when they are placed together in a spring unit, and which can be easily aligned. An evolution of the offset coils brought the elimination of the knot that tied the end of the wire to the coil. In other words, offset coils might be tied off or feature a loose end (sensory arm). These are called “open end offset coils”. These improvements gave offset coils an extra turn of working wire for greater spring action on each end of the coil.

Continuous coil

They look like double wire spirals or loose ringlets, creating a network of wire running nonstop through the entire bed. The brand Serta uses continuous coils in their mattresses. Kingsdown also uses such a system. The idea is that with a continuous coil system, each coil is connected to the next so that it can draw strength from it. This type of coil system does tend to be the strongest, however we must remember that strength does not dictate support.