Types of innersprings in mattresses

Mattress specifications

Understanding mattress springs

There are quite a few different types of spring units used in mattress manufacturing and they all have pro’s and con’s. Generally, the pocket spring unit is considered by most manufacturers and experts as the best type of spring unit for comfort and conformance and is generally used in premium style and more expensive mattresses. All of the Sherman mattresses use this type of spring unit but this article discusses all of the spring units available in mattresses in Australia.


(Also known as pocket coils or Marshall coils). Said to have been invented by James Marshall in Canada in 1899, this style of spring unit only became common in the 1970’s when manufacturers found a way to produce the style of spring unit en masse. Prior to this, the units were sewn together by hand.

Individual, floating coils of wire are encased in pockets of fabric that allow the springs to move independently of each other and contour extremely well to the sleeper’s body form. Mattress experts agree that pocket spring units provide unsurpassed support and comfort when compared to any other type of mattress spring unit.

Pocket springs in a frame for a pocket spring mattresses

A softer style of pocket spring unit can also be comfortable enough to sleep on long after the foam in a mattress has lost it’s comfort so you may be able to sleep on this style of mattress for a lot longer before needing to replace it.

Most good quality pocket spring units will have at least 600 individual pockets in a Queen size unit, which is more than enough to provide the appropriate support and conformity for all sleepers. Some manufacturers cram in more pockets and use this as a marketing feature. An example of this are Micro Coil overlays, which are tiny springs sewn into a sheet and layered on top of each other. Beware of this, as this doesn’t always bring extra benefits to the sleeper but almost always means that the mattress can be sold at a higher price.

An important note about pocket spring units is that due to the fact that the metal coils are not held together by anything else other than thin fabric, it is not the most durable of spring units. It is essential that the unit is surrounded by steel perimeter frames in order to keep the entire unit together. Without these perimeter frames, the outside rows can simply be pulled or ripped away and they offer little in the way of edge support.

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The Bonnell spring unit is what you will normally find in budget mattresses in Australia along with Single or King Single size mattresses. Manufacturers also use them in “Commercial Grade” mattresses under the premise that the springs are longer lasting than pocket springs. This claim may be true but can be negated by the fact that is the foam comfort layers that will always wear out before the mattress spring unit.

Bonnell springs in a mattress

The spring unit is made up of many hourglass-shaped coils, all tied together with rows of metal “helical coils” (these are long corkscrew wires that coil through the top of each spring as they are inserted across the top of the spring unit). The entire unit is then surrounded by perimeter frames at the top and bottom of the unit. Most Queen sized Bonnell spring units contain approximately 360 coils, but of course, can be manufactured with less or more, depending on the size of the coils and/or the quality of the spring unit.

The fact that the coils in the Bonnell unit are tied together comes at the expense of body conformity for the sleeper. Wherever you depress the unit, the surrounding coils will also be pushed down, unlike the pocket spring unit where the individual coils react independently of each other.

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Known commonly in Australia as an LFK spring and used most often by the Sealy company, the Offset Coil spring is a tied innerspring unit, similar to the Bonnell spring.  An offset coil unit consists of many springs that are tied together by  rows of metal “helical wires” (as a  Bonnell spring unit is, see above). The entire unit is then surrounded by perimeter frames at the top and bottom of the unit. As with any tied spring unit, movement and partner disturbance is an issue in mattresses using this style of spring.

Offset coil springs in a mattress

The main difference with this type of spring is that, rather than the top of the spring being circular, it is usually a hexagonal shape, which allows the springs to be packed in closer together. Manufacturers claim that this also allows the individual springs to conform more easily to the body, but the fact that each spring is tied together makes the claim dubious.

The individual springs in the LFK unit do not have knots at the top of each spring like the Bonnell coils, rather the end of the coil is left open and angled down into the coil.

LFK spring units will generally contain many more springs than a traditional Bonnell spring unit and is a very robust spring unit. Mattress salespeople will often steer larger-framed people towards a mattress using this type of spring because it will be sturdier than a pocket spring unit. However, that statement is open to question because the comfort in the foams will wear out long before any innerspring unit.

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Generally, this is the cheapest type of mattress spring unit to produce due to the fact that the entire unit is formed by one continuous wire, which is wrapped and shaped into coils in one mechanical motion. The top of each coil is then tied together by rows of metal “helical wires” (as above with the Offset coils and Bonnell springs). The entire unit is surrounded by perimeter frames at the top and bottom of the unit.

Continuous coils in a mattress

In a continuous coil unit, each coil may only turn two or three times, meaning that the unit does not “give” or respond to depression as easily as other types of coils. The entire unit can also consist of much less working wire than a Bonnell or LFK unit, which also contributes to it’s lower cost to manufacture.

I am not a fan of the continuous coil, in my mind it exists only as a way for manufacturers to cut cost out of a mattress. Ironically, this style of spring unit can sometimes be marketed as a premium style of spring but the truth is that there is simply no real benefit for a sleeper on a continuous coil spring (when compared to the other types of mattress springs).

The continuous coil is not as robust as the Bonnell or LFK spring units and will usually rock from side to side quite noticeably whenever the sleeper moves on the mattress.



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