The innerspring is by far the most popular style of mattress on the market today.
Despite the rise of newer materials like latex and memory foam, innersprings still account for about 2/3 of all mattress sales.
Not only are they the most readily-available mattress on the market, they’re also typically pretty affordable, and work well with a broad variety of people—stomach sleepers, people with back pain, and heavy people alike can all get a good night’s sleep on the right innerspring mattress.
For such a popular design, though, there’s a lot the average person still probably doesn’t know about what’s actually going on inside their innerspring.
There’s a lot of complicated terminology that gets thrown around when we start getting into the nitty-gritty of mattress sales, so it can be helpful to have a basic understanding of what we’re really saying when we start talking in terms of “comfort layers” and “coil gauges.”
So, here it is: your definitive guide to innersprings.
What Is an Innerspring Mattress, Anyway?
At its most basic level, an innerspring mattress is a mattress with a core of coils that provides support for your sleeping body.
Columns of coils are all packed together under several comfort layers, and when you lie down, they compress in response to your body’s weight to provide support exactly where you need it.
These coils are what give innersprings their characteristic bounciness and form-fittingness, and once you understand everything you need to about them, you’ll be well on your way to making informed decisions about innerspring mattresses of all kinds.
Basic Mattress Spring Coil Technology
Now, as with just about everything involving modern mattresses, there are a couple key terms that get used quite a bit once we start talking about innerspring coils.
The concepts aren’t all that difficult to understand, but it’s hard to really know what kind of innerspring you’re buying if you don’t understand its coils.
Let’s start easy, here.
Mattress coils, also known as springs, are curved pieces of high-density steel wire that compress and expand depending on where pressure is placed.
The support system in your innerspring mattress is made up of hundreds of coils, all arranged into tight rows to provide you with the support you need.
Another quick term to get a hold of, pitch refers to the angle of your mattress’s coils in relation to the top of the mattress.
Coil count and coil density
Respectively, these terms refer to how many coils you have inside your innerspring mattress and how densely these coils are packed.
Coil density is really the more important idea here, since obviously you’re going to need more coils to get good support on a California king mattress than you do on a toddler bed.
As a general rule of thumb, you want to avoid mattresses with coil counts that are too low, since they won’t be able to adjust to your body’s contours as well as you’d probably like.
Again, the specific numbers you’re looking for vary somewhat based on your mattress’s size: full mattresses should have at least 300 coils, queen mattresses need a minimum of 400 coils, and kings need at least 480.
Is more coils always better?
Well, expert opinions vary somewhat when it comes to this question.
Some say that greater coil counts increase contour ability, support, and durability up to a certain point.
Others, though, say that once a mattress has met a certain baseline coil count, adding more coils doesn’t do anything except increase the mattress’s price.
There are a couple things everyone agrees on, though.
First of all, if all else being equal, higher coil counts mean higher prices.
Second of all, heavier people are likely to appreciate higher coil counts, since they provide better support and strength.
Finally, don’t judge any mattress based on coil count alone.
There are a lot of different factors that go into a mattress’s comfort level, and coil count is just one number among many.
“Gauge” or “coil gauge” refers to the thickness of the wires that make up the coils of your innerspring.
(It’s also used to measure all kinds of different metal thicknesses, from electrical wires to shotgun shells.)
Now, be careful here, because the way we measure these things is actually a little counterintuitive.
The thinner a wire, the higher its gauge is.
The thicker the wire, the lower its gauge is.
For every one-digit increase in the gauge number, the thickness decreases by 10%.
That means that if, for instance, you’re purchasing a 12-gauge innerspring, the wires that make up your mattress’s coils will all be about 2.05 millimeters thick.
If your coils are 13 gauge, on the other hand, the wires will only be about 1.82 millimeters thick.
Mattress coils typically range from 12 to 15 gauge.
Higher gauge coils (thinner wires) will be softer and more forgiving, while lower gauge coils (thicker wires) will be firmer.
If you’re looking for a nice, soft mattress, look for coil gauges about 14.
If you prefer your mattresses firmer and less forgiving, on the other hand, get yourself a mattress with a gauge of 13 or lower.
Note that higher gauge coils are less durable than their thicker counterparts.
However, since you’ll probably need to replace your mattress long before its coil fatigue becomes too important, you don’t need to think too much about this when you’re considering a new mattress.
The Four Kinds of Innerspring Coils
With these terms out of the way, we’re now ready to take a look at your innerspring’s coil configuration.
The way the coils in your mattress are arranged can completely change a bed’s bounciness, pressure relief, and motion transfer, so pay attention to the kind of coils your mattress manufacturer is using!
Bonnell coils are the cheapest and most common option. These springs are designed in a characteristic “hourglass” shape, and they’re laced together to form Bonnell units (also called a single coil or uncoil system).
Bonnell coils’ hourglass design allows for both flexibility and support.
The wider portion flexes and conforms easily to your body when you first sink in, providing good initial support.
The tightly-wound center of the hourglass, meanwhile, is less responsive and offers a high degree of stability.
Bonnell coils are the cheapest type of coil, and also the least durable.
They’ll wear out in about three to five years of nightly use, so they’re a solid option for kids’ rooms, dorms, or guest rooms.
Like Bonnell coils, offset coils take an hourglass shape.
However, their heads are squared-off and linked together with bits of thin wire called helical lacing, which creates a hinging effect when pressure is applied.
This allows for better contouring.
Pocket coils, also known as Marshall coils, wrapped coils, or encased springs, are built individually wrapped in fabric sleeves.
This allows each of the springs to interact with your body individually, rather than an entire mesh of springs moving at once.
This allows for a more buoyant feel, and also minimizes motion transfer.
They do a very good job of conforming to the shape of your body, and a pocket coil innerspring is ideal for use with foundations or adjustable bases.
They’re not the most durable coil style, but your mattress’s comfort layers are going to give out before your pocket springs do.
Continuous coils are made of a single length of wire that is shaped into a series of S-shaped springs.
This allows the entire spring system to function as a single unit, allowing for a strong, stable, and durable mattress.
Note, though, that the continuous design allows for a lot more springs per mattress than other designs, so it’s hard to compare continuous coil counts to other kinds of innersprings.
In addition to their spring core, most innerspring mattresses also have a few inches of comfort layer.
There’s a lot to unpack about this piece of a mattress—too much for us to properly dig into right now—but basically, they provide an extra bit of padding and support as we sleep.
They also provide pressure relief for areas like the lower back that tend to sag when we lie down.
The three parts of a comfort layer
Most comfort layers have three parts: the middle upholstery, the insulator, and the quilting.
The topmost of these is the quilting.
his provides an extra layer of cushioning and thickness to the mattress, and also improves breathability and temperature regulation.
Below the quilting is the largest part of the comfort layer, the middle upholstery.
This is made of a soft, supportive material, and adds greater comfort as you lie down.
Finally, the bottommost portion of the comfort layer is the insulator.
This holds the middle upholstery in place, and also separates it from the core.
Comfort layer materials
There is a wide variety of materials any given comfort layer might be composed of.
Some common ones include latex, memory foam, polyurethane foam (aka polyfoam), natural fibers, micro coils, and gel.
The various pros and cons of each of these materials is a topic probably best left for another time, so for now, just try doing some of your own research and check out our extensive mattress reviews to see what mattresses will work best for you!
Conclusion About Mattress Innersprings
Armed with all this information, you should now be ready to take on the wild, wild world of innerspring mattresses.
Remember, though, that the components of an innerspring mattress can only really tell you so much about how it actually performs.
If you really want to see how mattresses perform in practice, you’ll want to have a look at some real reviews.
Luckily, here at Mattress Guides we have just the thing.
We’ve built an extensive, continuously-updated index of reviews on just about any mattress under the sun, and we’re always growing.
So if you feel like you now how a pretty good idea of what kind of innerspring mattress you’re looking for, just head over to Best Mattress Review and check out some of the our top picks!
Stacey is the co-founder of Mattress Guides and continues to recommend and review countless mattresses. Together with Ted, Stacey makes sure that thousands of people are sleeping well and wake up healthy and ready for the day.
Updated at November 6, 2020