Mattress Support Cores

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Introduction

Every mattress features an internal support system designed to improve spinal alignment and relieve pressure points throughout the body. This is known as the support core, and it works in tandem with the comfort layer to provide a suitable sleep surface. Like the comfort layer, the support core is an important consideration to make when looking at a new mattress ? and several different types of support layer are used in today’s mattress models. The five most common support cores are:

  • Innerspring
  • Latex
  • Polyurethane foam (Polyfoam)
  • Airbeds
  • Waterbeds

This article will examine the pros and cons for each of these support core types. These criteria include comfort, support, price, warranty, product lifespan, maintenance and eco-friendliness. For more information about mattress construction, check out our guide to mattress comfort layers.

Innerspring

Bonnell coils are the most common type of innerspring coil, and are distinguished by a rounded hourglass shape.

Innerspring support cores are found in the majority of mattresses sold today. These systems consist of steel springs, or coils, that are evenly placed throughout the core for optimal, consistent support. Coils are usually rendered from steel, then heated and cooled during a process known as tempering, which softens the metal for extra flexibility. The longevity of a coil’s springiness is known as temper memory. Coils located on the borders are often reinforced with foam, netting or other durable materials to protect against wear, since the edges of a mattress tend to begin sagging before the center area.

The coil count of most mattresses falls between 300 and 1,000, although some models have more than 2,000 individual coils; this number can be used to determine the level of support and contouring of a given mattress. Coil count is also tied to lifespan and overall cost. Mattresses with a high coil count tend to be more resilient, and thus more expensive, while those with fewer coils are usually cheaper. However, coil count alone should not be used to judge the overall quality of a mattress.

Other factors to consider when you are browsing innerspring mattresses include wire gauge, or thickness. This measurement is expressed using numerals that signify certain widths (per a standardized American measurement system); the higher the gauge, the thinner the wire. The wire in most innerspring mattresses will range from 17- (thinnest) to 12-gauge (thickest). It’s worth noting that gauge is not necessarily correlated with wire strength; wire gauge and coil count must both be taken into consideration. Additionally, the pitch, or the angle of the wire path in relation to the top surface, can be used to determine how firm the mattress will feel. And turns, or the number of times the wire is wound, will indicate how soft the coils are, and thus how supportive the mattress is.

Let’s look at the four most common types of innerspring mattress coil:

    • Bonnell coils are the oldest type of cushioning coil, and date back to the seat seats used in horse-drawn buggies. Bonnell coils are formed in a rounded hourglass shape; the top and bottom are threaded with corkscrew-shaped wires called helicals, which join them to adjacent coils, while the sides are usually grafted to heavy-gauge wire for added stability. The result is a durable coil that won’t shift too much when compressed; for this reason, bonnell spring mattresses are commonly used in hotels, dorms and other places that serve a steady stream of sleepers over a long period of time. Bonnell spring mattresses are widely available, and most are relatively affordable compared to other innersprings.
    • Offset coils are similar to bonnell coils, both in their hourglass shape and helical-joined configuration. However, the bottom of the offset coil is straightened; this creates a hinge-like motion when the mattress is compressed. Some innerspring mattresses feature double offset coils, which are straightened at both the top and bottom for added support. Another variation is the free arm offset coil, which (as the name implies) has a side or top that isn’t joined to neighboring coils. Regardless of the type of offset coil, this configuration is typically found in more expensive mattresses because the design can withstand high levels of compression for long periods of time.
    • Continuous wire coils consist of several rows, each one made up of a single wire length, and the rows are joined together by helicals on both sides. This configuration ? often in a trapezoidal shape ? is highly stable, but its contouring abilities are minimal. As a result, continuous wire innerspring mattresses usually have a long lifespan but are considered less supportive than other models. Prices for continuous wire mattresses are comparable to the cost of a bonnell coil mattress.

Pocketed coils are wrapped in fabric, and usually found in more expensive mattresses.

  • Pocket coils, which may also be called Marshall coils or encased coils, are wrapped in a cloth material, forming strands of fabric used to join each individual coil. This configuration does not utilize helicals or additional wire attachments; rather, the strands are attached using hot glue. This increases contouring and reduces motion transfer, or the amount of compression you feel when your partner gets up from or lies down on the other side of the mattress. The number of coils will range from dozens to hundreds in a single mattress. Generally speaking, pocket coil models are among the priciest mattresses on the market.

For a side-by-side comparison, check out the innerspring coil fact table below.

BonnellOffsetContinuous Pocket
ShapeHourglassHourglass with at least one straightened endStraight line of wireSpiral, with fabric encasement forming a cylindrical silhouette
JoinerHelicals, additional high-gauge wireHelicalsHelicalsHot-melt glue
GaugeVaries Low to HighMedium to HighMedium to HighHigh
Coil Count400 to 600600 to 2,000400 to 800800 to 1,200
Price$$$$$$$

Before investing in an innerspring mattress, here are a few inquiries to make:

  • What type of coils are used? Bonnell and continuous wire coils may have a longer lifespan, but offset and pocket coils are considered more comfortable and supportive ? and are usually more expensive.
  • What is the coil count? This number is misleading, since coil count will not necessarily indicate the overall quality of the mattress; as mentioned above, you should also look at the coil shape, wire gauge, wire turns and wire pitch. But you should test out a wide range of coil counts to find the innerspring mattress that’s right for you.
  • Does the price match the coils? A mattress with a high pocketed or offset coil count will, in most cases, be much more expensive than a model with Bonnell or continuous wire coils and a relatively small count. Check to make sure the price-tag reflects the innerspring construction ? this won’t always be the case.

Latex

Latex is considered one of the highest quality mattress components

Latex is a substance derived from the sap of the Hevea brasiliensis, or rubber tree. Due to its soft yet resilient nature and body-conforming abilities, latex is commonly used in both the comfort layers and support cores of mattresses. A latex support core contains an all-foam core, with no springs or other small parts. Once the latex has been processed, it is cut into uniform sections and then layered. Glue is sometimes used to bond the layers together. The term true latex refers to mattresses with a support core and comfort layer made of latex.

Two factors are used to classify latex, the type and the manufacturing process. Most mattresses use a composite of natural (or NR) latex and synthetic (or SBR) latex, which is derived from petrochemicals. This type is known as blended latex. In recent years, many mattress manufacturers have begun to offer latex models that do not contain any synthetic materials, substances or chemicals. The U.S. Department of Agriculture (USDA) will label these mattresses as 100% organic latex. A similar ? yet different ? type of label is 100% natural latex, which contains trace amounts of SBR latex. Support cores primarily or mostly made up of NR latex tend to be the softest and most comfortable, so expect these models to be more expensive than mattresses with blended or mostly synthetic latex.

Latex for support cores may be manufactured using two different processes. The oldest and most common is the Dunlop process, during which the sap is stirred, molded and baked. This allows sediment particles to gather at the bottom, while the rest collects on top. Dunlop processing results in dense, heavy foam that is exceptionally firm. The other process, Talalay, has been utilized since the mid-20th century. The latex is placed in a vacuum-sealed chamber and then deoxygenated, frozen and baked. This three-tiered system allows the foam to form a more uniform consistency, which makes it softer and springier as a sleep surface.

The softness or firmness of latex foam can be tested using a measurement known as impression load deflection, or ILD. Some manufacturers use the term impression force deflection (IFD), which is synonymous with ILD. ILD signifies the amount of force needed to compress the latex by 25% of its total width, and is expressed in numerals. High ILD ratings mean the latex is firm, while low ILD ratings indicate the latex is soft. In most true latex mattresses, the comfort layer will be a low ILD foam while the support core will have a high ILD. However, this is not a hard-and-fast rule; the ILD rating of a mattress support core may range from 14 on the low end to 44 on the high end. The table below features a breakdown of different ILD ratings.

CategoryILD MeasurementFoam Characteristics
Very Soft16 and belowMattress sinks extremely low, may cause discomfort for some sleeper
Soft19-21Mattress sinks considerably beneath most sleepers
Medium24-26Balances softness and firmness to a fairly even degree
Medium-Firm29-31Firm support with minimal sinking
Firm34-36Very firm with little to no sinking
Very Firm39 and upExtremely firm, no sinking whatsoever

As is the case with latex comfort layers, latex support cores are highly sought after and considered some of the best mattresses available. In addition to natural softness, body-conforming comfort and durability, the material is highly breathable and relatively cool for sleeping. A latex core also improves motion transfer. Latex is naturally hypoallergenic, as well, and is considered much more durable than other support core materials. Typically, the only downside to these mattresses is the high price tag. Expect to pay much more for a latex mattress than an innerspring, polyfoam, waterbed or airbed model.

Here are a few considerations to make if you are interested in purchasing a mattress with a latex support core:

  • What type of latex is used? Blended and synthetic latex is cheaper, but natural and organic latex is softer, more breathable and more eco-friendly. Natural and organic latex will also drive up the price by a significant margin.
  • What type of manufacturing process is used? The Dunlop process will be suitable if you prefer a firmer mattress, while Talalay mattresses tend to be softer and bouncier.
  • What is the ILD rating? Although ILD is more relevant for comfort layers, you may notice a difference in mattresses with a softer- or firmer-than-average support core.

Polyurethane Foam

Polyurethane foam, or polyfoam for short, is a synthetic material produced from polyol and isocyanate petrochemicals. Polyfoam is similar to latex, in that the material may be used in the comfort layer, support core or both. The foam is cheap and easy to manufacture, so the majority of mattresses made today have at least a small amount of polyfoam in the comfort layer and/or support core. In addition to mattresses, polyfoam is often found in furniture cushions, car seats, mattress toppers and sleeping pads.

Polyfoam is classified based on two criteria: density and compressive modulus. Density is calculated by dividing the mass of an object by its volume, and is expressed in pounds per cubic foot; this measurement will indicate how much compression the mattress can handle, which relates to both supportiveness and durability. Density should not be confused with ILD (see latex section), which measures softness or firmness. Compression modulus refers to the ratio of stress to strain in objects, and can determine how much compression is needed before the foam’s structure is permanently compromised.

When used together, density and compressive modulus are used to determine the quality, or grade, of polyfoam. There are currently three grades of polyfoam available: high resiliency (HR), high density (HD) and conventional. Check out the table below for more information.

Polyfoam GradeDensity (Pounds per Cubic Foot)Compressive ModulusAvailabilityPrice
High Resiliency (HR)2.5 lbs/ft3 or higher2.4 or higherLess common$$$
High Density (HD)1.5 to 2.5 lbs/ft32.1 to 2.3Common$$
Conventional1.5 lbs/ft3 or lower1.8 to 2.0Common$

Conventional-grade polyfoam will not provide adequate support for most sleepers, as the material will deteriorate quickly, and won’t conform to your body. If you have sleep issues or chronic pain and require a mattress that relieves pressure points, then HR or HD polyfoam will provide more comfort ? although even HR polyfoam is generally inferior to latex in terms of overall quality and support.

Not surprisingly, polyfoam grade is linked to price. Conventional-grade polyfoam is typically found in the cheapest (and least durable) mattresses sold today. HD polyfoam is often used for mid- to high-range mattresses, including those with comfort layers made of more expensive materials like latex or memory foam, an ultrasoft type of polyfoam used exclusively in comfort layers. Mattresses with HR polyfoam support cores are usually the most expensive ? and least common ? option.

Bottom line: while most mattresses feature some polyfoam components, models with polyfoam cores will not provide the same level of body-contouring support and comfort as mattresses constructed from different materials. However, this will be the best option if you are mattress-shopping on a budget, or you don’t require an especially supportive mattress.

Interested in a polyfoam mattress? Here are a few questions to ask before buying:

  • What grade is the polyfoam? The highest-quality HR polyfoam has similar qualities to natural latex, while conventional-grade polyfoam may fall apart after one year of nightly use. Make sure you’re not paying HR prices for HD polyfoam, as many expensive mattresses will feature HD polyfoam.
  • What type of comfort layer is used? In mattresses with polyfoam support cores, the comfort layer often makes all the difference. Models with thick comfort layers made of latex or memory foam will provide a much more enjoyable experience than mattresses with thin or cheaply made comfort layers.

Airbeds

In recent years, airbeds have become a popular alternative mattress choice. The support core construction is simple: a hollow chamber known as a bladder that contains the air and maintains consistent air pressure. The bladder may be constructed from a wide range of materials, such as PVC, nylon, urethane or rubber. Historically, the bladder has been limited to a single, undivided space. In recent years, however, some mattress manufacturers have introduced zoned bladders that feature several mini-chambers. The purpose of a zoned bladder is to support individual areas of high and low compression, resulting in a more customized and body-conforming fit. Additionally, tri-bed airbed designs feature three isolated chambers designed to independently support your legs, midsection and head.

Another key airbed component is the pump, which controls the firmness or softness of the mattress by taking in or letting out air. Traditional airbeds require manual pumping, but many of today’s mid- and high-range airbeds feature remote-controlled pumps. For ideal sleeping, the pump should be relatively quiet and operate efficiently.

While the novelty of an airbed will be appealing to some, these models cannot provide the same level of support as latex, innerspring or even HR polyfoam support cores. A common problem is sinking: because there is nothing material separating the comfort layer from the bladder, the mattress will often sag all the way to the support core. As a result, airbeds will not properly align your spine or provide pressure relief compared to a latex, innerspring or polyfoam mattress. Waterbeds (see below) are also considered superior to airbeds in terms of support.

The way airbeds are marketed and sold to the public has also led to customer complaints. Many airbeds are advertised with selling benefits that ostensibly drive up the price, such as zoned bladders or internal walls to minimize motion transfer. However, these features have not been proven to provide the same level of support as other mattress types. Nonetheless, ‘luxury’ airbeds will be quite expensive ? more than $3,000, in some cases.

Many airbed have lengthy trial periods (i.e., 90 days), but you must usually keep the bed for a certain amount of time before returning it. Airbed warranties have been criticized, as well; while many warranties extend 20 years or longer, the prorated coverage will typically kick in after two or three years, leaving the owner responsible for additional expenses down the road. For more information about the difference between nonprorated and prorated coverage, check out our mattress warranty guide.

An airbed could be the most suitable option for you, but we strongly suggest testing out a number of models before finalizing your purchase ? as well as other, non-airbed mattresses. Here are a few more considerations to make if you are interested in airbeds:

  • How is the bladder constructed? Single-bladder airbeds offer the lowest amount of individual support, while zoned bladders and tri-bed models provide a more customized fit for your body.
  • What kind of pump is included? Remote-controlled pumps are usually found in the most expensive airbeds, but most models available today will utilize mechanized pumps (as opposed to manual ones).
  • What is the trial period, and what are the terms of the warranty? Don’t be fooled by lengthy trial periods and seemingly generous warranties, particularly in expensive airbeds. Instead, use durability and construction to help determine which airbeds are accurately priced ? and which ones are too expensive.

Waterbeds

Hard-sided waterbeds come set in a wooden frame and placed on a platform.

Waterbeds were a popular fad among sleepers of the ’60s, ’70s and ’80s, and this type of mattress has enjoyed a minor resurgence of late as the technology has evolved. Waterbeds were originally made from vinyl, and most modern incarnations are manufactured using PVC. Waterbeds are usually classified as hard-sided or soft-sided. Hard-sided waterbeds are set inside a sturdy frame (usually made of wood) and placed on top of a platform; soft-sided waterbeds, on the other hand, are set in a foam frame and encased in fabric. The key difference is that hard-sided models comprise a full bed, whereas soft-sided waterbeds are meant to be used with existing bedframes and other furniture. Soft-sided models also use less water.

Waterbeds may also be distinguished by their internal structure. Like airbeds, waterbeds utilize a bladder containment system. Free flow waterbeds feature a single chamber for unobstructed motion; this results in a moving, often wavy sleep surface. Waveless waterbeds control water flow through interior walls or baffles for a more stationary surface. There is no proven therapeutic benefit for free flow or waveless waterbeds, and satisfaction will entirely surface preference; the thickness of the comfort layer will also affect how wavy or still the surface feels. The majority of waterbeds are heated, and the temperature for most can be manually adjusted.

In terms of pressure relief, waterbeds are considered superior to airbeds because the water forms a cradle for your body, as opposed to air, which simply sinks. This is especially true in soft-sided mattresses, as well as waterbed models with flexible bladders and/or soft comfort layers. Sleeping on water that is heated and temperature-regulated can also have therapeutic effects, as well. Another perk: waterbeds are exceptionally easy to clean.

The biggest downside to sleeping on a waterbed is spinal alignment, although this issue has been the subject of an ongoing debate. Some authorities claim that waterbeds offer superior alignment, while others believe waterbeds are the worst option for alignment. The general consensus: every sleeper is different, but the two most important factors are your individual weight (as well as the weight of anyone sharing the bed with you) and the bladder construction.

Cost and maintenance are two other issues linked to waterbeds. Most mattress retailers won’t sell waterbeds, which means you’ll most likely have to buy your waterbed wholesale and pay more than you would for a standard innerspring or latex model. The most common waterbed maintenance problems include leakage, water contamination and overheating. Waterbeds are also susceptible to punctures, which are costly to repair. Waterbeds are especially heavy compared to other mattress types, as well, and should be completely drained before they are moved in order to avoid a big mess.

The cost of a new waterbed will depend on several factors. Hard-sided waterbeds tend to be on the cheaper side, usually no more than $500 for unused models, while the cost of a soft-sided waterbed can range anywhere from $600 to more than $2,000. As with airbeds, beware of tempting warranties, since the nonprorated coverage will typically last for, at most, only three to five years. Trial periods for waterbeds usually fall between 30 and 90 days, but you will most likely be required to keep the waterbed for at least three weeks before it can be returned.

Does a waterbed sound like an interesting mattress option? Be sure to check into these details while you’re shopping around:

  • Is the waterbed hard-sided or soft-sided? Soft-sided models are considered to be of higher quality than hard-sided ones, and the price of a new waterbed should reflect this.
  • How is the bladder constructed? Motion is usually the most important factor for waterbed users: is the surface wavy, or does it remain relatively still? Be sure to test out free flow and waveless waterbeds to decide which type best suits you.

For more information about the way mattresses are constructed for sleepers, please visit our comfort layer guide.

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