Buying a New Mattress: Mattress Coil Quality & Innerspring Construction

The mattress core (Innerspring Coils or Foam) is the most important part of the mattress in supporting your body. The foundation supports the mattress and the mattress supports you.

The majority of questions that we receive here at Seattle Mattress are usually centered around the structural quality of mattresses. To that end, here is our best, most up-to-date scoop on mattress coils and Innerspring construction:

Five factors can influence the durability of mattress Innerspring coils:

1. the number of coils
2. coil shape
3. the gauge of wire used to form the coils
4. the number of turns in each spring
5. the distribution of the springs - this final effect will depend on an interplay of all the above factors. So, for instance, more coils aren’t necessarily better if they’re lower in quality.

Number of Coils & Coil Gauge

The belief used to be, that the more coils a mattress had, the more support it would give. Today, this is not necessarily true - the way that the coils are constructed is the main factor in determining the amount of support. Coil counts themselves don’t matter unless that is the only difference between two beds you are considering. The coil type/construction and steel gauge are much more important.

There should be a minimum of 300 coils in a double bed, 375 in a queen-size, and 450 in a king-size. But otherwise, more doesn't necessarily mean better - let comfort be your guide. Rest assured, that EVERY 10-year warranty mattress on the Seattle Mattress showroom floor is well within coil-count parameters for each specified type of coil mattress that we carry!

Most manufacturers stake claim as to having the best coil-to-gauge ratio. However, there are only five general types of coils. The thing to remember is that while there are many different manufacturers and some of them even develop their own coil systems; they all develop them around the same general specs, and most of them will be worn out in about the same amount of time (10 years) if they are put together correctly to begin with - and these days, mattresses are piled so high with comfort layers, the coils don’t have to work nearly as hard as they used to.

That’s why the best mattress for you comes down to personal preference and depends, among other things, on your size and weight, and whether you sleep alone or with a partner – and then you can judge the quality aspects of the bed.

Innerspring Mattress Coil Systems

Bonnell Innerspring
Mattress Coils

Bonnell Coil: These are the oldest and most commonly used type of mattress coil - they are descendants of the antique buggy seat coil. This hourglass-shaped wire coil is joined to adjacent coils by small wire spirals called helicals. They compress quite easily at first, but then get firmer the more they’re compressed (hence offering more support), resulting in a ‘soft but firm’ bed.

The Seattle Mattress
Offset Innerspring System

Offset Coil: This coil system is a descendant of the Bonnell coil. Its construction is similar to the Bonnell Coil, but it has a squared head - which in theory, enables the mattress to contour better. An offset coil is also slightly more cylindrical in shape than a Bonnell coil and is also laced to its neighbors by helicals. 

At Seattle Mattress, we use this type of coil in our SMC brand mattresses. Made in the USA by reputable bedding manufacturer, Leggett & Platt; this is a strong innerspring system with 5 turns as opposed to 3 or 4 so they don't have to work as hard, with an even stronger edge. They work great in our double-sided mattresses; and if they are consistently maintained via flipping & rotating, they often outlast our manufacturer's warranty.

Open-ended Innerspring
Mattress Coils

Open-ended coils: are joined together to form a spring system, but the top (and bottom, for a double-sided mattress) of each coil is free to move independently. This allows each coil to adjust to the weight on it, with the free-moving bit compressing relatively easily for comfort, and the body of the coil offering more resistance and therefore firmer support. Because there’s more turns -- and therefore wire -- in these springs, they tend to be more expensive than other coil systems. The more turns, the softer the bed and the longer the springs will last because the work is spread around.

Independent Pocketed Innerspring
Mattress Coils

Pocket Coil: Also called Independent Coil or Marshal Coil was invented by Simmons, and is an individually pocketed cylindrical spring wrapped in its own fabric “pocket”. This separation construction is designed to give the most contour of any spring support system, as well as lessen motion transfer between sleeping partners. Each coil works independently - each pocket coil absorbs the weight placed on it without distributing the load to other coils. Because of this, the coils may lose their elasticity and provide less support over time, especially for heavier people. This type of coil is a good choice for people with partners who toss and turn, because the motion separation may prevent waking from a deep sleep which is very important for your health and well-being.

The Therapedic "Therawrap" Individual Pocketed Coil luxury mattresses on the Seattle Mattress showroom floor are a particularly strong option for people looking for this type of Innerspring mattress, since they have been manufactured to be a stronger option for this type of coil. Because the coils do not share the stress of the weight of a body being on it, coils that are used most and hardest (where you are heaviest) will wear out quicker. However, for people who are relatively height-weight proportionate, these are excellent mattresses for reducing motion transfer and providing cozy comfort.

The biggest problem we see regarding these types of Individual Pocketed Coil mattress systems is what we hear in feedback from customers coming into our store from other mattress stores. They often come in specifically looking for this type of coiled mattress because they have been told somewhere else that this is the strongest coil on the market today. It's not, and if you and/or your partner are significantly overweight, this is not a coil that we would suggest for you. However, customers are often steered toward these beds at other mattress stores because they are often the most expensive coils - because each coil is wrapped in it's own pocket, more materials are required to make the unit, meaning they can get more money for it. Just be aware of the limitations for this type of Innerspring coil if you are drawn to one. You and/or your partner's weight plays a big role in how long these coils will last.

Continuous Innerspring Mattress Coils

Continuous Coil: The Continuous Coil was invented by Serta and is the coil featured in their best-selling mattresses, the Perfect Sleeper Collection. It is exactly what it sounds like – each row of coils is made of a single wire attached to the next row by helicals. This type of coil is often made into a lattice of coils rather than rows, allowing more coils per mattress than other constructions. This design allows each coil to deflect weight to a great number of springs resulting in less stress on each coil. Mattresses with continuous coils keep their shape longer.

It is very important to note that just because some of these Innerspring systems sound stronger than others, doesn't necessarily mean that you should exclude any of them from your mattress shopping list options. ABSOLUTELY EVERYTHING about buying a new mattress should begin and center around your comfort, health and well-being. NEVER purchase a mattress that feels too hard or too soft to you just because it is "the best quality" - you'll regret it. :)