Mattress coils are metal springs that are arranged in a layer to support a sleeper’s weight. There are several types of mattress coils, and they all have their pros and cons. Coils give mattresses their bounce, and they provide a cool sleeping surface because their design allows air to circulate. The best mattresses usually have a lot of coils, but coil count isn’t everything. Let’s take a look at the different types of mattress coils, so you’ll know what to look for when you shop for a new bed.
Bonnell Coils
Bonnell coils are the oldest type of mattress coil, and they are still popular because they are inexpensive and provide good support. Bonnell coils are often called hourglass coils because they are thin in the middle and wide at the top and bottom. The thin middle yields to even slight pressure while the wider top and bottom resist pressure. Bonnell coils are usually connected with helical wire (thin wire twisted to form a spring shape) to form a continuous layer.
This design has advantages and disadvantages. A layer of Bonnell coils provides a firm sleeping surface with excellent edge support, but it doesn’t handle weight transfer very well. If you toss and turn a lot during the night or sleep with a partner who is much heavier or lighter than you, Bonnell coils may not be the best choice. A layer of these coils can also be noisy. When mattresses squeak, it’s usually because Bonnell coils are rubbing against each other and creating friction.
Offset Coils
Offset coils have the same hourglass shape as Bonnell coils, but their tops and bottoms are square instead of round. When they are connected with helical wires to form a continuous layer, their square tops and bottoms work together like a hinge. Offset coils provide the same firm support as Bonnell coils, but they are quieter and more comfortable. Offset coils are much better at controlling motion transfer than Bonnell coils, and they do not create as much friction when they rub together. This means they are less likely to start squeaking after a few years of use. Offset coils cost more to make than Bonnell coils, so they are rarely found in budget mattresses.
Continuous Wire Coils
This type of mattress coil is made by twisting a long wire into a row of connected coils. Several of these coil rows are then connected with helical wires to form a sleeping surface. This coil structure is extremely stable and durable, but it can be uncomfortable and doesn’t control motion very well. Continuous wire coils are usually found in inexpensive mattresses or mattresses with thick comfort layers.
Pocketed Coils
Pocketed coils are made by wrapping individual mattress coils in fabric. The wrapped coils are then connected with glue or thread, but each of them can move independently. This design all but eliminates motion transfer and allows pocketed coils to contour to the shape of a sleeper’s body. Pocketed coils also make less noise because their fabric wrappings prevent friction and absorb sound, and they are often paired with memory foam in hybrid mattresses to provide support for side sleepers.
Another benefit of pocketed coils is their durability. Pocketed coils don’t have an hourglass shape like Bonnell or offset coils, so they have no weak spot in the middle. The downside of pocketed coils is their cost. They are more expensive to produce than Bonnell or offset coils, so they are typically found only in hybrid or premium innerspring mattresses.
Mini, Micro and Nano Coils
Standard mattress coils are between 6 and 8 inches tall, but mini, micro and nano coils are much shorter. Mini coils are about 3 inches tall, micro coils are usually about 1 inch tall, and nano coils are even shorter. These coils connect with helical wire to form continuous layers that are sometimes placed in foam mattresses to improve airflow and provide additional support. Mini, micro and nano coils are usually wrapped in fabric like pocketed coils, but they are more yielding because their smaller dimensions allow them to respond to pressure more quickly.
Mini, micro and nano coils are made out of high-gauge wire, but they can be as strong and durable as standard coils. These coils are most often found in hybrid mattresses, which may have several layers of them. Layers of these tiny coils can be placed on top of each other or can be sandwiched between alternating layers of foam.
Coil Gauge
Mattress coils are rated based on the thickness or gauge of the wire used to make them. The thickest coils are made out of 12-gauge wire, and 17-gauge wire is used to make the thinnest coils. Coils that use thicker wire are firm and durable, so you won’t find them in soft mattresses. For the best combination of comfort and support, look for a mattress whose coils use 13- to 15-gauge wire. Most people replace their mattresses long before the coils inside them wear out, so don’t worry if your mattress has coils made of high-gauge wire.
Mattress coils last so long because they are made from tempered steel. Steel is heated and cooled repeatedly during the tempering process, which improves resiliency and hardness. A mattress coil made out of tempered steel can support a great deal of weight and regain its original shape even after years of use.
Source: Alexey Kartsev/Shutterstock.com
Coil Count
Coil count is the figure that consumers often check first when they shop for innerspring mattresses, and it can vary widely. A queen mattress can have fewer than 400 coils or more than 1,000, and a king-size mattress can have even more. Another thing to bear in mind is that coils are not always distributed evenly in a mattress. Some mattresses have coils arranged more densely around their perimeters to provide additional edge support.
Finding the Right Mattress
Hybrid and innerspring mattresses contain layers of connected coils, and knowing how they work together to provide comfort and support could help you to find the perfect bed. If you sleep on your back or stomach and prefer a firm surface, a mattress with at least 400 coils made from low-gauge wire would be a good choice. If you sleep on your side, you will probably find a more yielding mattress with coils made out of high-gauge wire more comfortable.
