Mattress Coil Comparison
Mattress Spring and Coil Types

The coils inside a mattress, also known as the core or the innerspring unit, provide the main support for the body. Proper support is essential not only for a good night's sleep, but for maintaining a healthy spine. When considering the core of an innerspring mattress, there are a number of important factors: the number of coils used throughout the mattress, the way the coils are constructed, and the shape of the coils.

Is a Higher Coil Count Better?

You might have heard people say that the more coils there are in a mattress, the more supportive the mattress will be. While this can be true, coil count is not nearly as critical today as it once was. Manufacturers sometimes use this perception to 'game the system' by using flimsy coils but putting a higher number of them into the mattress. Ultimately, what matters more is how much total steel is in the coil unit, and how the coil unit is constructed. These factors will be much more important in determining the overall comfort and support of the mattress.

• A typical mattress contains between 250 and 1,000 coil springs. As a rule of thumb, the minimum number of coils you should look for in a mattress is 300 for a full, 375 for a queen and 450 for a king-size mattress.
• A mattress with a lower coil count might use thicker wire or other techniques to compensate for this, and vice versa.
• Mattress units can be zoned to provide more targeted support for your curves, and for heaver parts of your body.

How are Mattress Coils Made?

Gauge:

When discussing the coils of an innerspring mattress, the word "gauge" refers to the thickness of the wire used to construct the coil. Somewhat counter-intuitively, the lower the number, the "heavier" the gauge, and the thicker the wire — 12.5 gauge wire (very "stiff") is thicker and stronger than 16.5 gauge wire (quite "springy").

Working Turns:

Another important factor is the number of "working turns" in each coil, a measurement of how tightly the coil is wound. Coils constructed with a higher number of working turns will result in both a softer and more durable mattress, since the work of supporting your body is spread throughout the spring. Working turns can be counted by tracing the wire with your finger — each time your finger travels 180 degrees around the coil translates to one working turn.

Tempering:

Tempering is the process of heating and cooling the coils to ensure they retain their proper shape over time. Tempering at a higher temperature can also increase the rigidity of the coil. A "double heat tempered" coil has gone through that process twice, ensuring increased durability.

Types of Coils

There are two main coil designs used in modern mattresses: Pocket Springs and Connected Coils

Pocket Springs

In a pocketed spring design, each coil is wrapped in an individual fabric sleeve (or "pocket"). These sleeves are then attached to one another (typically with fabric, glue, heat-treating, and/or hog ties) in order to ensure the coils remain upright. While the pockets might be connected together, there is no direct connection from one coil to another. This enables each coil to be compressed independently of the coils around it.

Below: Coils in their fabric pockets

Are Pocket Springs Better?

As recently as 2010, pocket spring coil units (also known as Marshall coils) were found in a minority of innerspring mattresses. But since then, their popularity has grown substantially and pocket springs have become the most common type of coil design used in the mattress industry today. Many innerspring mattresses now use pocket springs, and the majority of hybrid beds use them too.

This individually encased coil design allows each coil to be compressed independently of the coils around it. There are several well-recognized benefits to this design that have fueled its popularity:

• Enhanced conformance. In order to achieve proper spinal alignment, the surface of the mattress needs to conform to the curves of your body. Because each pocketed spring can be compressed individually, this allows for more precise conformance. This can be particularly important for side sleepers, in order to accommodate your shoulders and hips, and can aid with pressure relief as well. However, it can also be helpful for some back sleepers, especially those with a larger lumbar curve in their spine.
• Improved motion isolation. With no metal connections running across the bed, a coil that is compressed on one side of the bed has little to no effect on the coils underneath the person on the other side of the bed. This results in better motion separation than other innerspring coil types, meaning that when your partner starts tossing and turning, you are less likely to be disrupted.
• Reduced noise. Squeaky coils can be another form of disturbance. Inside of a mattress, this happens most often when metal is rubbing up against other metal. Since the fabric encasements prevent metal from touching metal, there should be no squeaks or creaks in a pocketed spring coil unit.

On the flip side, pocket springs endure greater strain over time, since any given coil is unable to distribute weight to nearby coils for help in providing support. In addition, the additional conformance will not necessarily be beneficial for all sleepers — stomach sleepers, in particular, benefit from less conformance as a general rule.

Connected Coils

Connected coil units (also known as "open coils") were once the standard in the mattress industry, but are now much less common. Although they are most often used in lower-end mattresses today, this type of coil design is not inherently inferior and in fact has unique benefits relative to pocket springs. As a result, it is still used selectively in higher-end mattresses as well. Here are some key benefits of a connected coil design:

• More uniform support. Any weight that is applied to a connected coil unit is immediately distributed across the surface of the mattress. This means that there will be less difference between how much your heavier and/or pointier parts sink into the mattress relative to your lighter parts. This can be especially helpful for stomach sleepers, whose chief concern should be ensuring that their heaviest part (the hips) do not sink too far into the mattress.
• Enhanced durability. This point can be somewhat controversial, since many (if not most) connected coil units today are made for extremely low-quality and inexpensive products. These units do not offer good durability prospects, however that typically has more to do with their flimsy wire and shoddy manufacturing, rather than an inherent weakness in their coil design. When all else is equal, a connected coil unit has fewer points of failure, since each coil is able to recruit support from the coils around it. That gives this design an inherent advantage in terms of its durability.
• Higher bounce. Bounce is strictly a matter of personal preference , so this will not be an advantage for all sleepers. But a connected coil unit generally offers more bounce and easier repositioning than a pocketed spring unit.

Of course, connected coils also have disadvantages, which tend to be the inverse of the pocket spring advantages listed above. Most notably, the lack of conformance makes it less appealing for some people, especially curvier side sleepers. And the connections between the coils can lead to motion transfer across the bed, as well as the possibility of a "roll-together" dynamic.

There are also several different types of connected coil units: Bonnell, Offset, and Continuous

Bonnell Coils

The Bonnell coil is known as the original mattress coil. Based on 19th century buggy seat springs, it has an hourglass shape with a knot at each end. Today, Bonnell coils are still the most prevalent type of connected coil used in the mattress industry, though they are typically found in less expensive mattresses.

Offset Coils

Offset coils are another type of hourglass-shaped coil, however the circles at the top and bottom of each coil are flattened to create a hinging action within the mattress core. This design, found in more expensive mattresses, allows the mattress to better conform to your body, and tends to make offset coils less noisy than their Bonnell predecessors. It also allows offset coils to be connected to each other via helicals (corkscrew-shaped wires that run over the tops and bottoms of the coils), which prevents them from moving from side to side when compressed.

Below: Offset hourglass coils connected with helicals

Continuous Coils

Continuous coil springs are made from a single length of wire shaped into a series of loose S-shaped ringlets. The concept behind this design is that by attaching each coil to its neighbors, the mattress core will be stronger, more stable, and more durable. Continuous coil designs also allow for significantly more coils per mattress, making it difficult to compare coil counts with non-continuous coil systems. Today, this coil type is common mainly in very inexpensive mattresses.

Micro coils

Historically, springs have typically been found in the support layer of a mattress. But thanks to more recent innovations, coils can now be part of the comfort layers, too. Micro coils are small, flexible springs that can make up a layer near the surface of a mattress. They are usually designed as individual coils wrapped in fabric pockets that are sewn, glued or welded together to create a flexible surface.

Micro coils range in height from about 1" to 3" tall. In addition to being shorter, micro coils are narrower and made with lighter gauge wire than regular coils. The lighter, encased wire gives micro coils a softer feel, and the smaller size enables more springs to be placed into a given area, also enhancing softness. Depending on their diameter, smaller micro-coils are sometimes referred to as "nano-coils."

If pressure relief and motion isolation are important to you, micro coils are a good choice. They do a good job of conforming to your body’s contours. They also do a good job at isolating movement. Micro coils provide a good level of repositioning and overall responsiveness, cradling the body while creating a supportive, pressure-relieving effect for recessed areas of the body not in direct contact with the support layers of a mattress.

How Long Do Innerspring Mattresses Last?

The basic techniques and materials used to make innerspring mattresses date back centuries, and are time-tested. Assuming you buy a good quality innerspring or pocket spring mattress from a reputable brand and retailer, your new mattress should last in the neighborhood of 8 to 10 years. It could be more or less depending on your circumstances, sleep style and body weight, but a quality innerspring mattress should hold up well and resist body impressions as well as (or perhaps better than) newer-technology memory foam.