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What's an innerspring mattress?

Coils are a classic bed material that allow for a cooling and firm sleep surface.

a woman's hand squishes pocket springs Credit: Getty Images / Anastasiia Stiahailo

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Springs are practically everywhere—you can find them in things as big as cars and bikes, and as small as the humble mechanical pencil. Mattresses are no exception to this “spring fever.” Innerspring mattresses were among the first and most popular widely manufactured types of bed. The patent for bed springs as we know them today dates all the way back to 1869. But classic doesn’t automatically equate to better. Here’s the low down on sleeping on coils.

What you should know about innerspring mattresses

Before explaining what exactly “innerspring” means, you want to decide if this type of mattress is even a good fit for you. If you’re a hot sleeper, there’s no contesting it: A mattress that contains springs will likely be your best option. Innersprings reign supreme in the realm of cooling though hybrid mattresses are still better than solid foam mattresses. This is because the springs promote air flow, which makes them better at dissipating heat. They also can be better at motion isolation, but this perk is more variable than the cooling.

Low-cost innerspring mattresses may be tempting if you’re on a budget, but their budget price can mean budget quality and feel. Innersprings are major culprits of irritating pressure points, and may be too firm for some sleepers—side sleepers in particular, who have significant pressure points on their shoulders and hips, might find innersprings don’t give enough cushion.

What are innersprings?

a diagram of different types of springs, showing one that has an hourglass shape, and ones with knotted and loose ends
Credit: Getty Images / Ihor Kashurin

Different types of coils have varying shapes, and can also have different styles of knotting—or a lack thereof—at the top and bottom.

Remember those cartoons where you’d see an old mattress on the side of the road with springs poking out this way and that? That’s your classic innerspring bed. (Though, if you can see the springs, it’s beyond time to move on and upgrade your mattress.)

The number of coils in an innerspring mattress can widely vary, and differs from brand-to-brand. Some mattresses have hundreds, others have upwards of a thousand. The general consensus is that a queen-size mattress should have at least 400 coils. The coils can be made in a variety of sizes and with different gauges (or thicknesses of wire, where thicker equates to firmer feel). Some mattresses use upcycled steel, while others rely on newly minted coils.

As a single piece of twisted wire, the ends can be secured to another part of the coil, or bent into a level plane and left floating. When the springs’ ends are secured to another part of the spring, it’s called “knotted.” This provides a more stable surface and makes a mattress less forgiving overall, so it may be a good choice for folks who prefer a very firm sleep surface. When the tail is left loose, the springs are called “open-ended” (imagine an outstretched slinky). This design makes the spring more sensitive and better at adjusting to your body, which may appeal to those who like a slightly cushier and responsive bed. On top of open and knotted springs, there are three main types of coils you might run into while shopping for an innerspring mattress, each of which offers a different sleep experience.

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Bonnell coils

Bonnell coils are a traditional, common type of innerspring that's affordable to make and buy in mattresses. They have an hourglass shape, tapering in towards the middle as opposed to having a totally cylindrical structure, like a soda can. The shape allows them to compress at the center which purportedly provides cushion, while remaining sturdy and supportive on the sleep surface.

These coils are typically knotted to create a stable sensation. Within a mattress, the coils may also be laced together by crosswires called “helicals,” which provide even more stability and rigidity to the top of the mattress.

Offset coils

These coils may resemble Bonnell coils at first glance, but don’t be fooled. The difference is all in the shape of the top and bottom of the spring. Instead of having the rounded top that Bonnell coils do, offset coils typically have a semi-square top and bottom (which makes them look a little like coils that went wrong in the manufacturing process, if you ask me). The angular edges at the top and bottom of the coils allow for mattress makers to hinge them together, by connecting the straight edges parallel to one another, rather than interlacing them with wires. The hinged construction can make a mattress’s surface better at conforming to your body and responding to pressure. Offset coils can be knotted at the end, or left open—the hinge will still give them more ability to conform, though open coils will lend the mattress a more forgiving feel. This type of spring is newer and a bit less prevalent than Bonnell coils.

Pocket springs

a line of pocket springs, which are springs within fabric pockets
Credit: Getty Images / Alexey Kartsev

Pocket springs can make a mattress feel more forgiving by offering better individual adjustments to pressure.

Pocket springs are coils that are placed in individual fabric sacks, or pockets. Manufacturers claim that pocketed springs make the mattress surface more comfortable by allowing the coils to move and adjust to pressure individually, rather than as an entire unit or sheet of springs (as with springs that are hinged or connected via helical wire). In addition, there are generally a greater number of springs than within a mattress than Bonnell or offset springs alone, which may contribute to the springs' better ability to contour.

There are a number of pure innerspring mattresses that use pocket springs, like the Serta Perfect Sleeper mattress (which still contains some foam on the top and edges, but buyers can specify how many layers they’d like ranging from one to three). Where you’ll almost certainly run into pocket coils is hybrids. Mattresses in a box, like the Leesa Hybrid, Puffy Lux, and Saatva Original, all use pocket coils.

Getting an innerspring mattress online

The coiled construction of innersprings means they can’t be purchased as a mattress in a box (unless you’re shopping for a hybrid, which is another story). It’s more or less impossible to compress true innersprings into the dimensions you’d need to accommodate shipping due to the wire rails that run around the mattress's periphery and give it structure, so don’t be discouraged if you’re having a hard time shopping for this type of mattress online. And if you do see an innerspring mattress that comes to your door in a box … I would be suspicious and say you should probably steer clear.

The final verdict on innersprings

innerspring mattresses in a mattress store
Credit: Getty Images / JackF

Innerspring mattresses are easier to find in brick-and-mortar stores than online, because the springs are difficult to compress.

Innersprings offer targeted support and structure that foam lacks, and if you want a super firm mattress, they might be a good option. This type of mattress can also be better at isolating motion, so if your partner is an active sleeper and thrashes around at night, they’re worth considering. But in my opinion, hybrids, which bring the benefits of foam and coils together, will be a better option for most people.

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Prices were accurate at the time this article was published but may change over time.

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