Posted October 24th, 2014
By: Wesley Vaughn

Pocket Coils

Pocket (Marshall) Coils


Pocket coils
Image from Simmons Beautyrest

Pocket coils, also known as pocketed coils, encased coils, wrapped coils or Marshall coils, are light gauge open-end coils in fabric pockets.  They were invented in 1900 by James Marshall, an Englishman who migrated to Canada. In Toronto, Ontario, Canada he founded the Marshall Mattress Company to make mattresses using his technology.  The company is still in business, focusing solely on pocket coil mattresses.  It was featured in a 2011 BedTimes Magazine story.

Marshall Mattress Company, About

Marshall Mattress Company, original building

The pockets are attached to each other, but the coils are not.  This allows each coil to respond independently to weight place directly on it.  According to Brad Warner, owner of Marshall Mattress,  the pocket coils were invented to meet a need:   “Legend has it that Mrs. M. was bedridden and Marshall created the support system for her, with coils wrapped in unbleached muslin, quilted with horsehair and outer tufted.”

Pocket-Spring Patent Drawing Inverted

James Marshall’s patent drawing for pocket coils, Aug. 20, 1900

At first, since they had to be made and encased by hand, pocket coils cost so much to manufacture that they could be used in only the most expensive mattresses.  Then in 1925, Simmons engineer J. F. Gail invented a machine to make the coils and insert them into cotton pockets.  This reduced the cost of a pocket coil mattress enough to place it in the general market.

Pocket coils are now very common around the globe.   According to Marshall Mattress, “Marshall’s pocket spring-filled mattress system has become the original worldwide standard for spring-filled mattress construction and remains to this day.”


The main advantage of Marshall coils is the individualized support they offer.  The independent response of each coil conforms the entire unit to the shape of the user’s body, resulting in  even support for the entire body.  This means two things:
(1) Larger parts of the body do not bear a disproportionate  load.  This reduces or eliminates pressure points.
(2) In-between sections of the body are supported.  This keeps the spine in proper posture, relieving or preventing  back and neck pain.


Simmons was the first major bedding manufacturer other than Marshall Mattress Company to utilize pocket coils.  They are the heart of the Simmons Beautyrest line of innerspring mattresses.

Refinement of pocket coils is ongoing.  Relatively  recent developments are microcoils and dual coils.   Microcoils are short, small diameter pocket coils.  Though no industry-wide standard definition of microcoil has been set, the term is used for coils as much as 4″ tall.

Leggett & Platt "Softouch"  Microcoil

Dual coils are a coil-in-coil design, first patented in 2010 by Sealy engineer L. K. DeMoss.  The two coils are made of one wire.  They turn in opposite directions.  The outer coil is taller with fewer turns, making it more responsive.  The inner coil is short and has more turns, making it more supportive.  This configuration makes it more durable than the hourglass figure of Bonnell coils, which also have a dual response.


Another development in pocket coils is tall coils, some as much as 10″ high.  The objective of this development is to make the mattress less dependent on less durable comfort materials such as memory foam, latex, and foam in general, as well as reducing the overall height of ultra plush innerspring mattresses.

Though pocket coil technology is over 115 years old, the basic value of individually wrapped pocket coils along with continuing development of this form of innerspring support indicates that Marshall coils are here to stay.


Posted October 23rd, 2014
By: Wesley Vaughn

Continuous Coils

Continuous Coils

continuous_coils_looking down rows

Looking down rows of continuous coils
Image from Bedrooms & More, Seattle, Washington

Continuous coils are the least expensive type of coils used in innerspring mattresses. According to Seattle Mattress Company, this coil type was invented by Serta. Currently, Serta is the largest user of continuous coils. Serta‘s continuous coils are manufactured by Leggett & Platt under the trade name Miracoil. Continuous coils are among the five most commonly used innerspring coil systems. The other coil types are Bonnell coils, knotted and un-knotted offset coils, and pocket (Marshall) coils (which also includes micro-coils).

Continuous coils are so-named because an entire row of coils is formed from one continuous wire (see picture above). Each row is tied to the next row by a spiral (helical) wire. The wire forms one coil going up and the next going down, which means the coils are paired, The helical wire also links one end of a coil pair to the end of the next pair in the row (see picture below).

continuous_coil_innerspring unit

Continuous coil innerspring unit
Image from Bedrooms & More, Seattle, Washington

The benefits of continuous coils include affordability, durability, stability, and consistent support. They also enable greater coil density, which makes support smoother. As with other coil systems, the goal is to enable the users to experience quality sleep.

The principal drawback of continuous coils is that motion is transferred along the row. For this reason, coil rows usually run head-to-toe. The helical connection of one row to another acts like a hinge, providing more flexibility across the mattress to lessen motion transfer between sleeping partners. This also reduces the load carried by each individual coil.

Some mattress models have rows of continuous coils both lengthwise and crosswise. This significantly increases coil density, enabling the mattress to support more weight.

Most mattress models using continuous coils are in Serta‘s Perfect Sleeper collections. These were engineered in cooperation with the National Sleep Foundation.


Posted October 23rd, 2014
By: Wesley Vaughn

Offset (Karr) Coils

Offset (Karr) Coils


Offset Coil System Image from Bedrooms & More, Seattle, Washington

Offset coils, also called Karr coils, were invented in the early 1900s by Frank Karr, who also started the Spring Air mattress company. They were developed from Bonnell coils, the original support for innerspring mattresses. Since the inception of offset coils, they have been used by many other mattress companies.

Pair of offset coils
The principal distinction of offset coils from Bonnells is the shape of the ends. The top and bottom ends of Bonnell coils are round. Then they are tied into rows by spiral wires. The ends of offset coils are squared at opposite ends.  The squared ends of one coil are tied to those of the next coil with a helical wire.  This functions as a hinge, which allows each coil to respond individually, making an offset coil innerspring unit more flexible than a Bonnell.

The flexibility of offset coils reduces pressure points on protruding parts of the body, such as shoulders and hips.  This also means better back support, especially for side sleepers.  Additionally, this reduces motion transfer.  Alternating right-hand turning coils with left-handed ones makes the mattress more stable by countering any tendency to lean one direction or the other.

There are two basic forms of offset coils, knotted and un-knotted.  Knotted ones are more stable and have a smoother feel.  Un-knotted Karr coils are springier and more flexible.

offset_coil_innerspring_unitBecause they are more complex, offset coils cost more to make and assemble.  thus they are usually found in the more expensive higher-end models of mattresses. Those who can afford them value offset coils over Bonnell coils for both their durability and the quality of sleep provided by greater comfort.


Posted October 22nd, 2014
By: Wesley Vaughn

Bonnell Coils

Bonnell Coils


Bonnell Coil System,
Image from Bedrooms & More, Seattle, Washington

The oldest type of coil used in mattresses is the Bonnell coil.  Bonnell coil mattresses are often called “traditional mattresses” or “traditional innerspring mattresses.”  Other types of coils have been developed since, but they all originate in the Bonnell coil.

Bonnell coils themselves were developed from buggy seat springs.  They are hourglass shaped.  The ends are knotted, the end of the wire twisted around the coil wire, making a full circle (see the single coil in the illustration above).  The coils are attached to each other in rows by a helical wire (see middle picture).  And all the rows together in a heavy wire (or perimeter rod) frame form the innerspring unit.

The hourglass shape of a Bonnell coil gives it a dual action.  The narrower middle is “softer” with an initial yield  when a weight is placed on it.  Then the wider ends increase resistance for “deep down” support.

The narrow middle section is a weak point in this type of coil, making it prone to distortion or breakage leading to mattress sagging.  Nevertheless, Bonnell mattresses give good support when new.  Thicker-gauge wire and/or a less-pronounced hourglass figure make a Bonnell coil more durable.  At the same time, this makes the innerspring firmer.  This is the reason Bonnell coils are usually found in firmer mattress models.  A taller coil or fewer turns can make heavier-gauge coils less firm without sacrificing durability.

Bonnell coils cost less to manufacture and assemble than other types.  Therefore they are usually found in lower-priced entry level innerspring mattresses.  If a sleeper or a couple are not too heavy, a well-designed and made Bonnell coil mattress can last a reasonably long time.


Posted October 18th, 2014
By: Wesley Vaughn

Rayon (Viscose)

Rayon (Viscose)



A sample of rayon from a skirt, photographed with a macro lens. from Wikipedia                          _____________________________

The oldest man-made fiber is rayon. It is formed of dissolved cellulose extracted from wood. Although almost any woody plant can supply the wood, some of the more common sources were conifers such as spruce, hemlock and pine. That was when most rayon was produced in North America and Europe. Now that the largest producer of rayon is in India, woods from that part of the world are commonly used, including bamboo. In fact, several bedding manufacturers advertise that the rayon they use is made from bamboo.

Artificial cellulose fibers were first made in France in the mid-1800s. Textile producers and fashion designers were looking for a substitute for silk in response to a silk shortage. In 1885, Count Hilaire de Chardonnet patented the first process for making fibers from dissolved cellulose. This process was too expensive for large-scale commercial production. In the early 1900s the viscose process was developed. A thick cellulose liquid was made after several stages. This viscose could be extruded as sheets (cellophane) or fibers.

Since two radically different forms were produced, the Federal Trade Commission sought a separate name for the fibers. Sometime between 1920 and 1926 the name rayon was coined. Probably because the fibers were shiny, the ray was for light. The -on may have been added for cotton, or it may be from the French word for ray: rayon. Now rayon commonly refers to the fiber and viscose for the liquid. However, in Europe the fiber is usually called viscose, for example Magniflex mattresses, and that has been accepted by the FTC as an alternate name for rayon.

The FTC has also ruled that bamboo rayon is not the same as bamboo fibers, and the names of the materials should reflect that.  Therefore, rayon from bamboo can be called that or bamboo rayon, but not bamboo fiber(s).

Though rayon is made from a natural, renewable product, the process of extracting the cellulose poses environmental problems of air and water pollution. However, the process is being refined to reduce the waste products in the hope it will eventually become environmentally acceptable.

Rayon has many advantages and uses. It is durable, visually appealing, dyeable, versatile. Because it is cellulose, it has properties similar to those of cotton and linen. It is also now less expensive than cotton, which has its own environmental problems from cultivation. In fabrics, it can be made to resemble cotton, silk or nylon. Rayon has been displaced by polyester in some uses, but it is still a commonly used fiber, especially in bedding materials, such as mattress covers.

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Posted August 29th, 2014
By: Wesley Vaughn



Polyester Fiber (Wikipedia Commons [PD]), from photo by Edward Dowlman, taken at Strathclyde University


Polyester, sometimes just called “poly,” is a long-chain polymer.  According to the Federal Trade Commission, a polymer has to be at least 85% esters to be classified as polyester.  There are several kinds of polyester, but the kind abbreviated PET is made into fabrics.  PET is also the substance of plastic beverage bottles, which can be recycled into fabrics.

Polyester is made by reactions of alcohols and acids, usually derived from petroleum or coal.  The initial reactions were discovered in the 1930s by W.H. Carothers, a DuPont chemist, who found that when carboxyl acid and alcohol were mixed they could produce fibers.  Nylon was developed at the same time, so polyester was forgotten for a while.  But in 1941, British chemists rediscovered the reactions and began producing polyester fibers.  DuPont bought the rights in 1946 and began developing polyester for textiles.

Polyester 500px-Transesterification

Polyester (also called “poly”) began to be used in clothing in 1961 as Dacron.  It was washable and wrinkle-free, needed no ironing, kept its color, and dried quickly. It could also be blended with natural fibers, such as cotton or wool, making them wrinkle-resistant and more durable.  Poly-cotton is a commonly used fabric today.  The ratio of polyester is usually between 15 and 65 percent.

Polyester and poly-cotton are frequently used in mattress covers.  Of  bedding manufacturers reviewed on Beds.Org, at least 33 use polyester or poly blends in their cover materials.  At least one manufacturer, WJ Southard, refuses to use polyester.

Besides fabrics, filling and insulating material (also called “polyfill”) are made of polyesterPolyester fibers can be any shape the extrusion nozzle can be cut into, even hollow tubes.  It can be heat set to any shape, such as crinkled.  Tubular and crinkled fibers are highly insulating as well as filling. Several mattress manufacturers use polyfill, often in the quilting.

For now it appears that polyester is here to stay, blended with natural fibers or on its own.  It offers desirable qualities at affordable cost.  It is also easily recycled.  It can be designed to have the characteristics of natural fibers, such as cotton, linen, wool or silk.  It can also imitate the semi-synthetic fiber rayon (extracted wood cellulose).  As to being a petroleum product, it may someday be made from plant-derived materials.


Posted August 28th, 2014
By: Wesley Vaughn

Box Springs

box spring (USM)

Box Spring (from US-Mattress)

Box Springs

A box spring is a sturdy frame–usually wood–on which springs are mounted.  The frame and springs are covered in cloth, usually with padding on the top and a base pad on the bottom.  According to the Merriam-Webster online dictionary, the first known use of the term “box spring” was in 1865.[1] The term box spring is sometimes alternatively spelled box-spring.  Making it one word, boxspring, is generally not acceptable.

Traditionally, the springs are metal.  They may be coils or corrugated spring wires (repeated “S” curves).  The purpose of a box spring is twofold:  provide sturdy, resilient support for the mattress, and elevate the mattress to a convenient height.  The box spring has some give, making it more resilient than the floor.  This way it absorbs some of the shock when someone bounces into bed (or on the bed).  This extends the life of the mattress.  It also protects the floor.

There are a number of ways of attaching/inserting the springs in a box spring.  For example, some companies, like Shifman, tie them eight ways.  Some are just stapled to the frame and clipped to an upper grid.  The amount of handwork going into making a box spring partially determines its cost.  Also factoring into the cost are the gauge of the spring wire and the metal used, as well as materials for the cover and padding.


Hand-tying box spring coils (Shifman Mattress Company)

It is also easier for most people to get into bed when the sleeping surface is several inches off the floor.  The standard height of a box spring is 8 to 9 inches.  However, with higher mattresses now in the market, low profile box springs and foundations of 4 to 5½ inches are available.

Once the only foundation other than a bed frame, a box spring is now only one of the foundations available to mattress customers.  Other foundations are platforms, wood slats, and adjustable beds.  However, most retailers list foundations other than adjustable beds as box springs.

A European wood slat foundation can be legitimately considered a box spring.  Instead of metal, the springs are slats of highly resilient wood.  With the development of wooden coils, these may someday be found in box springs.  Foundations filled with foam are called box springs by some firms.

Most manufacturers of mattresses make their own box springs.  The box springs are designed to work with their mattresses.  Therefore, the best box spring is the one that is sold with that mattress.  Also, a box spring can wear out, just like a mattress (it can also be accidentally damaged in handling), so it is best to buy a new box spring for a new mattress.

[1] Ecyclopædia Britannica, Merriam-Webster, “box spring,”, 
accessed 08/27/2014.

Posted August 23rd, 2014
By: Wesley Vaughn

European Wood Slats

ESW mattress_materials_slats_02

European Wood Slats –

In Europe, the preferred foundations have several closely spaced slats made from a springy wood, such as beech.  The resiliency of the wood makes the wood slat foundation absorb shock, much like a box spring.  The springiness  of wood can be felt walking over a wooden floor as opposed to a concrete surface.

Unlike the box spring, a wood slat foundation does not depend on metal, making it preferred by persons wary of the amplification of electromagnetic radiation (radio waves).  This same motivation inspired the recent development of wood springs.  Wood slat foundations are now being made and sold by mattress manufacturers in the United States, such as European Sleep Works (ESW).  The “Flexible Slat System” made by ESW is adjustable so the users can make it customize the response.

There are bed frames using wood slats which do not qualify as European wood slat foundations because the slats are not close enough to each other.  In other words, the gaps are too wide.   With a slat foundation, if the slats are spaced closely enough they can be used for memory foam mattresses.  They also provide better support for innerspring mattresses as well.  No matter the kind of mattress you have, it needs adequate support to help support you, the user, and to extend the life of the mattress.

A wood bed frame with widely-spaced slats can very well elevate a foundation, but it cannot take the place of a well-designed, closely-spaced European wood slat foundation.


Posted July 29th, 2014
By: Wesley Vaughn

Phase-Change Materials (PCMs)

Phase-Change Materials (PCMs)

stack-of-icecubes-277x300 (BedTimes)

Ice Cubes (from Bed Times Magazine)

Consumers now occasionally see the terms “phase-change materials” or “PCM s” in descriptions of clothing or bedding.  Each season, more manufacturers use PCMs in their products, some even making them a selling point.  Even a casual reading tells us that phase-change materials have something to do with comfortable temperatures.  More exactly, PCMs are used to keep temperatures within a desired range.  But what are phase-change materials, and how do they work?

What Are Phase-Change Materials?

According to Wikipedia, “A phase-change material (PCM) is a substance with a high heat of fusion which, melting and solidifying at a certain temperature, is capable of storing and releasing large amounts of energy.”[1]  All materials absorb heat when they melt or vaporize and release heat when they condense or freeze, but not all materials qualify as PCMs.  A phase-change material absorbs and/or releases large amount of energy in the process, remaining at the same temperature until the process is completed.

How Do Phase-Change Materials Work?

As a solid substance absorbs heat energy, it becomes warmer, eventually becoming hot enough to melt.  Wax is a good example.  We have all seen light wax becoming soft on a hot day.  Only a little warmer and it reaches the melting point.   As the wax melts, it absorbs heat from its surroundings.  As it solidifies, it releases heat. When the air becomes cooler (or the source of heat is removed), the wax cools by releasing heat.  Cool enough, it becomes solid again.

Changing PCMs (Illumin, USC )

Canging PCMs (Illumin, USC )

The most well known and longest used phase-change material is ice.  A container of water will not fall below 32˚F (0˚C) until all the water is frozen, and that ice will not rise above 32˚F (0˚C) until completely melted.  Ice is more efficient for keeping things cold than water is for keeping them from getting too cold; it takes 144 times more energy to melt 16 oz. of ice than to raise the temperature of 16 oz. of water by 1˚F. [2]

Large bodies of water have a moderating effect on nearby land, and ice is perfectly fine for keeping food and drinks cold, but it is too heavy, bulky and messy for controlling temperatures in mattresses and clothing.  Lighter substances which are easier to handle are needed for this, as well as materials that can release enough heat at the lower end of the preferred temperature range.

How Were Phase-Change Materials Developed?

In the 1970s and 1980s NASA wanted to protect instruments in spacecraft from extreme temperatures without using large amounts of energy to operate heating/cooling systems.  The most feasible means was to use materials which would absorb or release large amounts of heat when needed, and phase-change materials were the ideal solution.  PCMs were used on the SkyLab and space probes.

After this, NASA sought to apply this technology to spacesuits to protect astronauts on extravehicular excursions.  Engineers at Triangle Research & Development in Triangle Research Park, NC, developed means of incorporating PCMs in textile fibers. Using this under license, Outlast Technologies is marketing fibers and fabrics to manufacturers and users of textiles, including bedding producers.[3]

What Phase-Change Materials Are Used in Bedding?

PCMs in Fabric (Illumin, USC)

PCMs in Fabric (Illumin, USC)

Phase-change materials used in textiles are generally in the form of microencapsulated gels or polymer chain links.  Since many of these substances are irritants, the means of application depends on whether the user has body contact with the material with PCMs.  With no skin contact, coating–which is the most efficient method–is used.  Most of the phase-change materials used are polyolefins (waxes) whose melting points are in the desired ranges.  Several PCMs are usually selected and balanced to narrow the effective temperature range to a comfort zone for sleeping.

Phase-change materials in mattresses and pillows are not restricted to the fabrics.  For instance, a patent assigned to Sleep Innovations by inventor Walter Mackay is for a method of incorporating certain types of  PCMs (“organic compounds of nonmetals other than C, H, O, and N”) into bedding foams.[4]

Considering Phase-Change Materials in Shopping for Bedding

The use of phase-change materials is one available choice when shopping for a mattress, pillows, or other bedding products.  Whether you select a product with this feature depends on several considerations.  Availability is no longer a major consideration since so many brands now incorporate PCMs into their mattresses

The first consideration is, “Will this really help me sleep better?”  This depends on how temperature affects your sleep, which in turn depends on the ambient room temperature (how you use heating or air conditioning) and the composition of the mattress.  Mattresses with foams, especially memory foam, tend to be warmer, sometimes too warm.  If your bedroom tends to be too warm or too cool, or if the top layers of your mattress have memory foam, PCMs may be the solution to keeping cool.

The next consideration is cost.  Phase-change materials are now so widely used that the cost is not as high.  Some mattresses with PCMs, such as the Serenity Gel by Bed In A Box, are in the low-to medium price range.

The most important consideration–not to be forgotten–is, “Does this mattress meet my needs, regardless of whether or not it has PCMs?”

[1] “Phase-Change Materials,” Wikipedia,
[2] “Melting to Keep Cool,” PBS Nova,
[3] Mansfield, Richard G., “Phase Change Materials,” Textile World,
[4] Patent Docs,


Posted July 27th, 2014
By: Wesley Vaughn



Many of us have heard of the Silk Road. The name conjures images of adventure, romance, luxury, wealth, conquest and intrigue.  It was the route from China to India, Persia, Egypt and Europe by which silk was carried to market.  In ancient times, China was known as the Land of Silk. That is where production of silk began some time before 3500 b.c. In fact, our word “silk” came from the Chinese word si.   China is still the major producer of silk, producing about 3⅓ times as much as second place India.

Silk Road

The Silk Road

Silk is a natural fiber, made by silkworms, the larvae of the Mulberry Moth (Bombyx mori) and a few other moths.  The Mulberry Moth of China and the Ailanthus Moth (Samia Cynthia) of India are the only completely domesticated silk moths.  The mature larvae spin cocoons to protect themselves in the pupa state (when they undergo metamorphosis, changing into adult moths).  Silk is the thread that makes the cocoon.  The cocoon is boiled to kill the pupa and loosen the thread, which is then unwound and reeled.


Silk-producing moths

Silk is a smooth, shiny material.  It is very strong, and exceptionally long fibers make it even stronger. It is also very fine.  A single fiber is hard to see.  Most silk threads are composed of several fibers.  Silk textiles are strong and durable.  They are used not only in clothing, but in parachutes, luggage, draperies and upholstery.

In bedding, silk has long been used in sheets and pillowcases.  It is also used in cover fabrics for mattresses and foundations.  Sometimes silk is the sole fiber in a mattress ticking or cover (as in the Natural Silk Elegance by BedInABox), but often it is blended with other fibers, such as wool (as in the World Luxury series by King Koil), bamboo (as in the Tempur-Contour Allura by Tempur-Pedic) or cashmere (as in Stearns & Foster’s Lux Estate and Lux Estate Hybrid collections).

Besides its strength, silk is a breathable fabric.  It is also absorbent.  The fibers wick moisture away to evaporate, keeping the surface of a mattress both dry and cool.  Silk is also resistant to most acids, making it very durable.  Silk has another benefit from a marketing standpoint.  With the reputation of silk, just naming it among the component materials of a mattress lends a perception of luxury.

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